Our pre-reception was at 10 am - 11 am, and our reception was from 11 am - 3 pm. I figured since it was so early in the morning I didn't want to pay for a full bar when most people wouldnt be drinking. I paid for the non-alcoholic drinks (soda, water, juices) from 10 am - 2 pm, and had a cash bar for the entire time. We knew all of our guests pretty well so we knew noone would be offended or care either way, and it worked out great in my opinion! I gave my guests plenty of notice that if they wanted to buy alcohol to bring some cash, and I think only about 5 or 6 of the guests really took advantage of that.
Most of our guests actually left around 2 pm anyway (most had to head to the airport right away or had their kids with them who were exhausted from being up since 6 am), so I'm glad we didn't pay for the last hour of drinks. (I had a feeling that would happen so planned accordingly).
I think the mimosa idea sounds great!