It is supposed to be supported according to the documentation. However like many things written in the docs, it is not necessarily accurate. I found that delays less than a second are entirely dependant on the processor load.
I used this to compensate for a while but it too would occasionally go tits up. I don’t bother any more.
Edit: ah! while milliseconds may be a valid option it is pointless specifying this. Home assistant works on a 1 second resolution for delays in automations and scripts.