Are you asking if you can go 2x a week and why he wont allow it or that you want to pick a second backup option in case the first usual time isn't available?

If it's the first, idk, you have to ask. My T sadly works for a place that wont allow anything beyond 8 weeks at 2x a week. All crisis stuff gets you passed on to crisis lines etc. It sucks but I've just had to learn to manage alone on the tough times.

Each T is different, it could also be an insurance issue or maybe he just doesn't think you need it that often. Some people are lucky and can do 2x a week for a long as they want, wether it's needed or not. Others can't There is no all around same thing for this, each T/company decides differently

IF its the second, no idea, again, ask but it seems odd that they would not be open to a second option unless they truly are THAT busy all week