The Home Office requirement is that you must collect your BRP card within 10 days of arrival in the UK. 
However, where you have tried to do so and failed (i.e., there is a delay in the delivery of your BRP) or where the University booking availability is limited or dated for a future large-scale event which you plan to attend, then you can rest assured that it is acceptable to wait and delay collection, until it is logistically possible to collect your BRP card.