Originally Posted by gnomey

(all these are explained in the official evisa website FAQ, I am only paraphrasing)

the only rules are

- you enter india via selected airports or seaports within the 30 days validity period of evisa's ETA

- once entered on date N, the true 30 days stay clock begins

- you must exit on date M, which is N+29. otherwise you will be considered overstaying

- the earliest one can apply for a 30 day evisa's ETA is 30 days before intended entry. the latest is 4 days before

- the expected processing time for an evisa ETA application is 1-3 days.

you can do whatever you want based on the above constraints

the above do not apply for other kinds of evisa duration. why india makes it so complicated I have no idea.