Dropping crib mattress?

Nicole • Baby #2
FTM here and am wondering when I should drop the crib mattress. My baby is almost 5 months and can roll over very well. She loves to stand when I'm holding her but can't pull herself up yet. She can only sit up unassisted for like 10secs at a time. Should I drop it now or do I still have time? It seems like a big jump from one level to the next.