Working Preggy Mom here.

Ay mama, depende talaga sa type ng work mo and how you're feeling! Most of my preggy friends took leave around 36-37 weeks para makapag-rest ng konti bago magbaby, pero may iba naman na nagprestige until labor na dahil hindi gaano demanding ang work nila. Since you're almost at 31 weeks, you still have good time to plan, maybe coordinate with your OB kung ano ang best timing para sa iyo, and also check with your company kung ano ang maternity leave policy nila. The important thing is you're not overexerting yourself these last weeks, kaya if you're exhausted na talaga, wag mag-hesitate to go on leave earlier!