This hook pmpro_checkout_start_date allows you to change the start date of a membership before checkout.

apply_filters( "pmpro_checkout_start_date", $startdate, int $user_id, object $pmpro_level );

Parameters

$startdate

$user_id

int;

$pmpro_level

object;

Source

File: https://github.com/strangerstudios/paid-memberships-pro/blob/master/preheaders/checkout.php

File: https://github.com/strangerstudios/paid-memberships-pro/blob/master/services/ipnhandler.php

File: https://github.com/strangerstudios/paid-memberships-pro/blob/master/services/twocheckout-ins.php