diff --git a/src/config.ml b/src/config.ml
index e3c112ee..827fe57f 100644
--- a/src/config.ml
+++ b/src/config.ml
@@ -128,9 +128,9 @@ module Coin = struct
   type t = {
     section_name: string;
     value: Amount.t;
-    duration_withdraw: Ptime.Span.t;
-    duration_spend: Ptime.Span.t;
-    duration_legal: Ptime.Span.t;
+    duration_withdraw: Timestamp.span;
+    duration_spend: Timestamp.span;
+    duration_legal: Timestamp.span;
     fee_withdraw: Amount.t;
     fee_deposit: Amount.t;
     fee_refresh: Amount.t;
diff --git a/src/denomination.ml b/src/denomination.ml
index 7b296362..ae561bd9 100644
--- a/src/denomination.ml
+++ b/src/denomination.ml
@@ -36,16 +36,14 @@ let make
       Config.Coin.t) =
   assert (cipher = `RSA);
 
-  let stamp_start = Ptime_clock.now () |> Option.some in
+  let stamp_start = Timestamp.now () in
   let stamp_expire_withdraw =
-    Timestamp.add_span_exn stamp_start (Some duration_withdraw)
+    Timestamp.add_span_exn stamp_start duration_withdraw
   in
   let stamp_expire_deposit =
-    Timestamp.add_span_exn stamp_start (Some duration_spend)
-  in
-  let stamp_expire_legal =
-    Timestamp.add_span_exn stamp_start (Some duration_legal)
+    Timestamp.add_span_exn stamp_start duration_spend
   in
+  let stamp_expire_legal = Timestamp.add_span_exn stamp_start duration_legal in
 
   let open Mirage_crypto_pk.Rsa in
   let priv = generate ~bits:rsa_keysize () in
diff --git a/src/management.ml b/src/management.ml
index 2f6d19f4..2767e139 100644
--- a/src/management.ml
+++ b/src/management.ml
@@ -196,15 +196,11 @@ let update_master_signatures ~db_conn ~sm_signkey ~sm_denom
           match opt with None -> error | Some v -> Ok v
         in
         let check = function false -> error | true -> Ok () in
-        (* TODO time *)
-        let timestamp_equal a b =
-          let timestamp_to_int64 = function
-            | None -> None
-            | Some v -> v |> Ptime.to_float_s |> Int64.of_float |> Option.some
-          in
-          timestamp_to_int64 a = timestamp_to_int64 b
+        let* () =
+          check
+            (Timestamp.to_int64 valid_from
+            = Timestamp.to_int64 denom.stamp_start)
         in
-        let* () = check (timestamp_equal valid_from denom.stamp_start) in
         let* () = check (coin = denom.value) in
         let* () = check (fee_refund = denom.fee_refund) in
         let* () = check (age_mask = denom.age_mask) in
diff --git a/src/parse_config.ml b/src/parse_config.ml
index 0fd672a3..fb079846 100644
--- a/src/parse_config.ml
+++ b/src/parse_config.ml
@@ -173,9 +173,7 @@ module Parse_duration = struct
         (fun acc { number; dunit } -> acc + (number * dunit_to_seconds dunit))
         0 t
     in
-    let acc = Int64.of_int acc in
-    let ptime = ptime_span_of_int64 acc in
-    ptime
+    Timestamp.span_of_int64 @@ Int64.of_int acc
 
   let parse s : duration_element list =
     match parse_string ~consume:All duration s with
diff --git a/src/pg.ml b/src/pg.ml
index d958c6a6..70a1e99a 100644
--- a/src/pg.ml
+++ b/src/pg.ml
@@ -20,9 +20,10 @@ module Caqti_type = struct
         Amount.make ~sign:None ~currency:Config.currency ~value ~fraction)
       (t2 int64 int32)
 
-  (* we want to use int64 timestamps,
+  (* ! do not use ptime
+     we want to use int64 timestamps,
      not postgresql built-in timestamp type *)
-  let ptime : Ptime.t option t = Timestamp.caqti
+  let ptime : unit t = Caqti_type.unit
   let time = Timestamp.caqti
   let age_mask : int t = Caqti_type.int
   let rsa_public = RsaPublicKey.caqti
diff --git a/src/signkey.ml b/src/signkey.ml
index 883dfa93..e07eba70 100644
--- a/src/signkey.ml
+++ b/src/signkey.ml
@@ -12,10 +12,9 @@ type t = {
 }
 
 let make () =
-  let stamp_start = Ptime_clock.now () |> Option.some in
+  let stamp_start = Timestamp.now () in
   let stamp_expire =
-    Timestamp.add_span_exn stamp_start
-      (Some Config.Exchange.signkey_legal_duration)
+    Timestamp.add_span_exn stamp_start Config.Exchange.signkey_legal_duration
   in
   let stamp_end = stamp_expire in
   let priv, pub = Mirage_crypto_ec.Ed25519.generate () in
diff --git a/src/timestamp.ml b/src/timestamp.ml
index 710ac992..bb061c90 100644
--- a/src/timestamp.ml
+++ b/src/timestamp.ml
@@ -1,6 +1,8 @@
 type t = Ptime.t option
 type span = Ptime.Span.t option
 
+let now () = Ptime_clock.now () |> Option.some
+
 let diff a b =
   match (a, b) with
   | None, _ | _, None -> None
@@ -56,9 +58,31 @@ let ptime_of_int64 i =
   | None -> Fmt.failwith "ptime_of_int64 error: `%Ld` is not a valid ptime" i
   | Some ts -> ts
 
+let ptime_span_to_int64 span = span |> Ptime.Span.to_float_s |> Int64.of_float
+
+let ptime_span_of_int64 i =
+  match Ptime.Span.of_float_s (Int64.to_float i) with
+  | None ->
+      Fmt.failwith "span_of_int64 error: `%Ld` is not a valid ptime span" i
+  | Some ts -> ts
+
+(* - *)
+
 let encode_int64 = function None -> Int64.max_int | Some p -> ptime_to_int64 p
 let decode_int64 i = if i = Int64.max_int then None else Some (ptime_of_int64 i)
 
+let encode_span_int64 = function
+  | None -> Int64.max_int
+  | Some p -> ptime_span_to_int64 p
+
+let decode_span_int64 i =
+  if i = Int64.max_int then None else Some (ptime_span_of_int64 i)
+
+let to_int64 = encode_int64
+let of_int64 = decode_int64
+let span_to_int64 = encode_span_int64
+let span_of_int64 = decode_span_int64
+
 (* UINT64_MAX represents "never". *)
 let bin = Bin.map Bin.neint64 decode_int64 encode_int64
 let bin_nbo = Bin.map Bin.beint64 decode_int64 encode_int64
diff --git a/src/timestamp.mli b/src/timestamp.mli
index ae81b3a3..4da82338 100644
--- a/src/timestamp.mli
+++ b/src/timestamp.mli
@@ -2,15 +2,20 @@
    uhuh!
    need to be int64 for binary/pg round trip *)
 
-type t = Ptime.t option
-type span = Ptime.Span.t option
+type t
+type span
 
+val now : unit -> t
 val diff : t -> t -> span
 val add_span_exn : t -> span -> t
 val of_span_exn : span -> t
+val of_int64 : int64 -> t
+val to_int64 : t -> int64
+val span_of_int64 : int64 -> span
+val span_to_int64 : span -> int64
 
 (* - *)
 val jsont : t Jsont.t
 val bin : t Bin.t
 val bin_nbo : t Bin.t
-val caqti : Ptime.t option Caqti_type.t
+val caqti : t Caqti_type.t