This year's UI spring game kickoff is at 1pm CST. Admission is free, I believe. Specialists usually hit the field to warm up 1 to 1.5h before kickoff. I believe the stadium gates open at 11:30am.
The team typically goes through warmups and drills, then usually plays 11 on 11 for several series including refs/time-clock, etc.
I think the game offers a big opportunity for recruiting, in that the recruits see: 1) Kinnick with people in it (the more, the better, IMO); 2) the team outside, working with coaching staff on position drills and full 11-11 as well. It's a different atmosphere than the spring practice held in Des Moines, with typically 4-5x more people there. It's more like a regular season game, in that there's tailgaiting/vendors. When recruits don't attend a regular-season game, they typically tour the facilities including Kinnick, but it doesn't provide the impact that it does when the team and fans are present.
In response to the OP, there will be several recruits in attendance (see Tom K post on the topic as to who will be there).