Microcentury sounds like somebody didn't reduce their fractions. I propose centiyear.
Those are not the same; one is a bit less than an hour, another is 3 and a half days.
A microcentury is 100 nanoyears if you prefer that.
It's actually 100 microyears!
Erm, yes. Yes it is...
It's one ten-thousandth of a year but there's not a prefix for that.
100 microyears?