The Predraft has always been held during the week usually on a Tuesday or Wednesday. The main reason is because it is college tournament time and by Tuesday there is not much basebal;l being played. This allows the Scouting Directors, crosscheckers and other scouts the best time to attend. It is a "heavily" scouted event, that has had a lot of early draft picks attend. It is for top players from high school and college. One year we had brothers attend... Brian McCann was in HS, older brother Brad was in college. Yes, it is during school time, but it is a very important event for those who attend. Atleast two players who have attended, McCann and Carl Crawford (DRays) have been MLB ALL Stars already.
The unsigned and academic do get a nice turnout of colleges. Mostly higher level academic schools and colleges still looking for another player or two. It has worked out well for some players in the past. In the past colleges range from DIIIs to some of the top DI powers from the SEC and ACC.