Workout schedule

I am on a M_W_F swim schedule, try to walk on T-TH, also a walk on weekend. Three days a week at the Y is about all I have time for. I may be in trouble, trying to do this distance training but not having the time to invest. Only on Saturdays will I have time to swim for more than an hour at a time. I have to get rest between swims, as I am no spring chicken any more. I don't want to wind up injured or sick. It will work out.