Is it permissible to delay responding to messages from female colleagues on WhatsApp—messages related to studying and academic assistance—until there is time and psychological energy to respond, or is it obligatory to reply immediately upon seeing the messages?

Leaving messages unanswered or questions unaddressed is not forbidden (haram). However, it is desirable (mustahabb) to assist those in need if possible, provided no harm is incurred. Withholding assistance (preventing the ma'un) is of two types: that for which a person is sinful, which is what is obligatory to give, and that for which one is not sinful but misses out on good, which is what is not obligatory to give. It is advised to be keen on what benefits and to assist others within one's capacity, without incurring harm in matters of religion or worldly life.