I'm a 2014 UCR grad, I applied for 2014-2015 cycle and wasn't admitted or interviewed. But since I recall things coming pretty soon after submitting my primary that cycle I was surprised when August hit and I hadn't received one yet. I thought that was late and maybe I had slipped through the cracks.
Since I submitted day 1 through AMCAS, I was hoping ucr would send a secondary in the first group of schools. On August 7th, I sent them am email asking if I was forgotten, explaining that the school was high on my list, alumnus stuff, etc.
Well, that was on a Friday night and Monday morning I had a secondary invite in my inbox. If this school is important to you (and you can genuinely explain why) try shooting them a brief email or ask if there's an expected time frame for secondaries.
And yes, this school's secondary is difficult, (similar to UCLA or UC Irvine, I can't remember) but I guarantee they read all of it. I graduated with honors, worked multiple jobs on campus, research, honors program, etc. I honestly believed just being an alum with great scores and on-campus activities would get me in the door (especially given the 24 seats thing).
I was wrong.
Make sure you fit their mission statement. I thought my large amount of on-campus activities were a huge plus, but they told me they really want to see people active in their community outside of that.
btw I'm still waiting for II but I'd be glad to help with any other questions about the school, campus, city, etc.