There's no 'increment' property for this Spin Edit control.
The [+] and [-] buttons seem to only change it by +/- 1. If you want something that deals in milliseconds, then 10 or 100 is a reasonable increment value to use.
If you want to change the increment value in code, you need to trap the [+] and [-] button clicks, but there are no events for them.
Something seems to be missing here.
Also, I don't remember ever having a floating point value in a spinner. They've always been integers.