When you resize the Amazon RDS DB instance, Amazon RDS will perform the upgrade during the next maintenance window.If you want the upgrade to be performed now, rather than waiting for the maintenance window, specify the option.
ApplyNow
ApplySoon
ApplyThis
ApplyImmediately
Explanations:
“ApplyNow” is not a recognized option for immediate upgrades in RDS.
“ApplySoon” does not exist as an option in Amazon RDS for immediate upgrades.
“ApplyThis” is not a valid option in the context of RDS upgrade processes.
“ApplyImmediately” is the correct option to perform the upgrade now, bypassing the maintenance window.
I estimate that the answer is:
ApplyImmediately