the main issue for you is not the scheduler itself, but that usually the UEs in the simulator are modelled as full-buffer users. That means, you cannot determine the delay from that and also can’t prioritize messages.
To do so, you have to turn on traffic models, as you can find in LTE_sim_main_launcher_demo_trafficmodels.m. You will also then have to adapt the MU-MIMO scheduler such that it can deal with UEs that are not full-buffer (see e.g., +scheduler/PropFair_Traffic.m).
If you have further questions, please let me know!