NIH IRTA

I'm applying to a few post-bac programs and I was wondering, specifically for NIH IRTA, if you get accepted or interview for a lab, do they expect you to be able to commit on the spot?

For example, if I'm applying to other programs (I don't hear back until next March), should I start reaching out to PIs within the next month? And if I hear back from any of them, just tell them I have to wait until mid-March?

Alternatively, should I wait to reach out and start emailing PIs in the early Spring then?

Thanks!