Recently for unknown reasons smartthings removed the ability to add a new mode through the mobile app. I find it strange, but it's what happened.
You can still add a new mode through the IDE. Instructions are in the following thread:
As far as the automation, the official SmartThings features don't really do a "while" construct. However, there is a community – created rules engine that can do exactly that.
Setup is somewhat complex, but there are many community members who will be glad to help you.