Terms for "half a decade"
This website says the last lustrum was held in a.d. 74 by Vespasian. So I would say, no, lustrum is not the word you're looking for. Pentad is not in some dictionaries, and the one I found that does have it defines it as "a group of five". So that's not the word you're looking for, either. I would suggest
5 yr span
if you're trying to squeeze it into as short a space as possible. Quinquennium does mean what you want it to, but it's quite rare and fairly long.