I have resigned..Manager told to get retained and gave excel to fill and send him. Does revised Letter come instantly or wait for April?

Till u get ur new compensation don't revoke

Don't take your resignation back unless you get revised compensation letter or a mail from HR detailing how much will it be and from which date ?

Otherwise they will make fool.of you and after April you will get nothing

Revised letter usually takes time, not instant. April sounds about right for it to arrive