My gynae only gave me leave from week 36 onwards, so I'm not sure about week 33 being a hard rule lah. I think it really depends on your doctor and how your pregnancy is progressing - some give earlier if there are complications or if you're really struggling, but most seem to wait till closer to term. Best to ask your own gynae what they recommend for your situation, since they'll know your health better than anyone else.
usually gynaes give only week 37 or 38 and after. if you have a normal healthy pregnancy, nothing warrants hospitalisation leave. you can only get HL earlier if your pregnancy is a high risk one or not going well - you probably would not want that scenario.
It depends on your condition and gynae. Not sure if your gynae is strict. Some gynaes will only issue from week 35 onwards or even later. Week 33 might be too early to issue hospitalisation leave.