You shouldn't have to wait for your 3pt to work.
The manual does however say you should wait for the hydro oil to warm up before using any hydraulic attachments. If not warmed up you risk damaging the system.
I just partly disassembled my L245DT 3pt control cylinder.
I replaced the smaller of the two big o-rings on the cylinder cover which if leaking internally will disable your 3pt. I also replaced the control screw which was seized also disabling the 3pt hitch.
Don't snap that screw it's $54. It's the one between your legs under the seat with the knob.
Kubota's corporate site has all the system/parts breakdown for your tractor.
There's not a that can go wrong so you should be able to trouble shoot it.