IMHO, hard mode just get Lefty if you can, set him and just wait it out in the room next to the office. But yeah, that need to be adjusted. As it stands, it's not realistic to try and get tasks done on hard mode since the girls at the moment their walking paths is too random (though a helpful bug appears if the girls try to go to the same place at the same time). If the area was bigger or there were ways to hide this wouldn't be a problem but giving each girl a definite pathway would be best right now.
Normal mode, it's possible to get task done but the window is really tight. First set all the girls, get the bottles and condoms, open both doors, set all the girls again and then rush out doing one task at a time. For bathroom and wine refill, do half on one trip and the other half on another trip. On your final trip, don't worry about the girls at all. Luckily when they first start roaming they give you some time (Frenni dances on stage, Fexa sits in bed for a while, Chiku checks the microwave). If you know they are coming, either hide out in the electric room from the story mode, the bathroom, the storage next to office or make a break for the kitchen after Chiku leaves it.
It's far more difficult in 0.1.3 when you have to deal with Bonfie and the microwave can no longer be set on the cameras but has to be done in person. So now you have to add visiting the arcades and kitchen in your laps around. Sometimes I let one girl wonder just so I have less to keep track of and just try and keep my eye on her. Another thing that can be fixed on is the tablet, it'll be far easier if you can press a number key and go straight to a certain cam instead of going through them one by one.