hello
For early flowering id say 55 isnt bad since its couple with warm temperatures. You can usually run a higher humidity as long as the temp doesn't drop drastically at lights out....that's when pm wants to start growing, is with temperature Or humidity fluctuations.
If you have an outlet to bring in fresh air through a window or something using the intake fan that'd be best. Otherwise just keep running the dehumidifier, and keep the airfow up and water in the mornings, no late night waterings.