There is at no point, no matter how experienced you are, that you would not prepare to open an airport.
It is not a sign of how experienced you are as to how long it takes you to prepare either. Everyone should do as much preparation work as possible before opening.
Even the most decorated of controllers still prepare for hours and even days before opening to have the best understanding of the airspace in order to properly.
No one should ever be discouraged or told that it’s ok not to prepare, nor is it common within the controlling community.
There may common practices one uses, simple strategy that are interchangeable at every airport. But controllers should not become complacent, thinking they have no room to improve.
There is always room for improvement, controlling is a constant learning experience. Prepare beforehand and not during.