Mentor Calls are provided within 24-72 hours. Right before the examination, since people like to submit tests at one go and seek frequent mentor calls. This can increase to upto 3-5 working days. However, most of the Mentor Calls are closed with 1-2 working days.
Please note that you must whitelist the number from which you receive the call from ForumIAS for Support / Mentorship Issues. Please read this article as to how to whitelist ForumIAS Numbers