Minecraft wiki entry for schedule, associated text: Specify the delay time.
Must be a time in Minecraft. It must be a single-precision floating point number suffixed with a unit. Units include:
d: an in-game day, 24000 gameticks;
s: a second, 20 gameticks;
t (default and omitable): a single gametick; the default unit.
The time is set to the closest integer tick after unit conversion. For example. .5d is same as 12000 ticks.