There are no time-limits to book the GRE slot. You can visit the ETS site and book any date and slot of your choice provided it is available; this can be 90 days. Planning starts when to take GRE when to book GRE date, when to shortlist universities and when to apply. The first step to being focused on is GRE. Getting a. How to book slot for GRE? I will try to give a step by step guide on how to book a date for your GRE exam. Step 1 Go to the official website of.