1) Is tax deadline 5-17-21 even if I don't owe any taxes but getting a refund? 2) Can I submit payment to my IRA when I file my tax or must be deposited on 5-17-21?

the custodian must credit your account for the contribution on or before May 17.

go to a branch office in person, with funds, if you don't have an IRA.

Otherwise make a deposit online now.

if you are sure you will get a refund, you can't be late until three years have passed. Then it is too late.

The tax filing and payment deadline is May 17, 2021. The deadline to fund your IRA for 2020 is also May 17, 2021 (see @fanfare post immediately above)

Penalties for filing late are based on the tax due - if you are getting a refund, the late-filing penalty is "0".