You can use floating-point numbers in sleep():

The argument may be a floating point number to indicate a more precise sleep time.

So

time.sleep(0.5)

will sleep for half a second.

In practice, however, it's unlikely that you will get much more than millisecond precision with sleep because operating systems usually only support millisecond sleeps and because very short amounts of time quickly get unreliable.

You have not told us which sleep() function you are using.

If you are using the one in the time module then it does support fractional times.

https://docs.python.org/3/library/time.html#time.sleep

time.sleep(secs)

Suspend execution of the calling thread for the given number of seconds. The argument may be a floating point number to indicate a more precise sleep time. The actual suspension time may be less than that requested because any caught signal will terminate the sleep() following execution of that signal’s catching routine. Also, the suspension time may be longer than requested by an arbitrary amount because of the scheduling of other activity in the system.

#!/usr/bin/env python

import time

now = time.time()

for i in range(10):
   time.sleep(0.2)
   print(time.time()-now)

Results in

$ ./st.py
0.200302839279
0.400612831116
0.600860834122
0.801117897034
1.00143289566
1.20173883438
1.4020190239
1.6023080349
1.80258703232
2.00286793709