Can I pay Stamp Duty by Mar 21 at reduced rate of 3% and then sign the sale deed agreement in Apr 21 and then register

Q: Hello, I have purchased flat from MHADA (Govt org) in Mumbai. I have paid the full amount of Flat to MHADA. Now only Stamp duty, Sale deed Agreement and registration work is pending. Due to current situation, I am not able to come to Mumbal to Sign the sale deed agreement. I will be able to come in Apr 2021. Meanwhile Can I pay the stamp duty online at 3 % by 31st March 2021 and then sign the sale deed agreement with MHADA in next month. Or if I sign the agreement post March 21, I have to pay stamp duty at 5%.
Pls also advise me if I pay stamp duty now, sign the agreement in Apr 21, then max limit to register the documents is 04 months from the date of agreement..?

Thanks in advance