Can I use the Unicom broadband that I just renewed immediately?

It depends on where you connect Unicom broadband. If you are Unicom broadband in Fujian, you won't stop before the broadband expires. If the broadband has expired, it needs to be renewed. Under normal circumstances, it can be used normally within 24 hours after the successful renewal. Then if you use Unicom broadband from other provinces, I suggest you ask where Unicom's own business hall broadband is, or call Unicom's customer service broadband.