I suggest to convert all the work items into minutes, add them up, convert the result to hours and subtract from the time of leaving.
mowing 1hr15min=75min
trimming = 40 min
mulching = 25 min
shower = 30 min
total = 170 min = 2 hr 50 min
subtract 2 hrs from the departure time 2:00 to get 12:00 noon.
Then subtract the remaining 50 minutes from 12 noon to get 11:10am