If you look at the registration of the iPhone 15 and 15 Pro in the Bureau of Indian Standards (BIS), last year:
A first set of devices was registered on August 16, either the Pros or the regular ones.
A second set of devices on August 25.
Announcement: September 12
Pre-orders: September 15
Availability: September 22
If we take into account these intervals and Apple's propensity to announce such devices on a Tuesday, I'd say:
A second pair of devices will be registered next week, and then:
Announcement: April 23
Pre-orders: April 26
Availability: May 4
... and this would also line up with Gurman's report