I have 13 miles to go. I allow an hour for that. Then half an hour to get up, dress. eat. and load the bike. I add another half hour safety margin in case of flat tires and to change when I get to work. Two hour total. When it is raining I take the bus most of the way which adds another half hour.

Another time when I had a 20 mile ride to work I needed one and a half hours to get there and put in another hour for before and after so 2 1/2 hours. 1 3/4 hours getting home due to headwinds in that direction.