RUT on certain i50 buff potions not consistent with delve

The i50 elixir of speed delves with a 5s RUT just like other stat buff potions. Ditto for the i50 shard skin potion. However using one of these right before the other causes the second one to fail with a message "wait 55 seconds" or whatever. Appears that the RUT is really 1:00 on these, just like the combined forces one. (Tested this only in Mid but I'd expect same everywhere.)