diff --git a/src/timestamp.ml b/src/timestamp.ml
index a63d74d1..b567ec8a 100644
--- a/src/timestamp.ml
+++ b/src/timestamp.ml
@@ -1,36 +1,43 @@
-type t = Ptime.t
-type span = Ptime.span
+type t = int64 option
+type span = t
 
-let span_of_int_s = Ptime.Span.of_int_s
+let never = -1L
+let of_uint64_us us = if us = never then None else Some us
+let to_uint64_us = function None -> never | Some us -> us
 
-let span_of_int64_us us =
-  let s = Int64.(to_int (div us 1_000_000_L)) in
-  span_of_int_s s
+let to_s us =
+  if us = never then None
+  else
+    let s = Int64.unsigned_div us 86_400_L in
+    Some s
 
-let span_to_int_s = Ptime.Span.to_int_s
+module Span = struct
+  type t = span
 
-let span_to_int64_us span =
-  match span_to_int_s span with
-  | None -> None
-  | Some s ->
-      let us = Int64.(mul (of_int s) 1_000_000_L) in
-      Some us
+  let of_uint64_us = of_uint64_us
+  let to_uint64_us = to_uint64_us
+  let to_s = to_s
+end
 
-let of_int_s s = Ptime.of_span @@ span_of_int_s s
-let of_int64_us us = Ptime.of_span @@ span_of_int64_us us
-let to_int_s t = Ptime.Span.to_int_s (Ptime.to_span t)
+let compare = Int64.unsigned_compare
 
-let to_int64_us span =
-  match to_int_s span with
-  | None -> None
-  | Some s ->
-      let us = Int64.(mul (of_int s) 1_000_000_L) in
-      Some us
+let now () =
+  let d, ps = Ptime_clock.now () |> Ptime.to_span |> Ptime.Span.to_d_ps in
+  if d < 0 then Fmt.failwith "Ptime_clock.now negative ptime"
+  else
+    let d = Int64.(mul (of_int d) 86_400_L) in
+    let us = Int64.(div ps 1_000_000_L) in
+    Int64.add d us
 
-let now () = Ptime_clock.now ()
-let add_span t span = Ptime.add_span t span
-let sub_span t span = Ptime.sub_span t span
-let diff a b = Ptime.diff a b
+let add_span t span =
+  let us = Int64.add t span in
+  if compare t us > 0 then None else Some us
+
+let sub_span t span =
+  let us = Int64.sub t span in
+  if compare t us < 0 then None else Some us
+
+let diff a b = if compare a b < 0 then None else Some (Int64.sub a b)
 (*
 (* microseconds since the UNIX Epoch, or "never" if None *)
 let jsont =