hourly storage lockers in chicago?

Im going on a cross country vacation this winter and one of the stops is in Chicago. We arrive at 9am at the union station and won't leave until 5pm. We need a place to store our bags for those 8 hours and I want to know if there are any hourly storage places near by. I know there are storage lockers at the union station but it wouldn't be enough for the full 8 hours if i rent a jumbo locker for 3 hours reaching the 12$ limit and my partner renting another locker for 3 more hours. we would need to put our bags someplace for 2 more hours and if we both max out our lockers then where can we put our bags? Or am I reading it wrong and I can just rent a different locker after i max out the 3 hours for the first locker? And if i get the lockers for the 12$ max do i need to come back every hour to renew it? or can i just pay 12$ and come back after 3 hours?