/time add wont work

Can you please screenshot the commands you used?

I tried the following:
/time set day
/time add 15000
and observed that it got dark.

it was exactly /time add 4
does it have to be a five digit number? or do you think it was lag?

/time add 4 would be so tiny that it would be un-noticable! - try a larger number

You increased the time by 4/24000 day.
The clock in minecraft goes from 0 = morning, 6000 = noon , 18000 = midnight.
Closing this issue.