How fast does the rating deviation increase?

Usually it is very hard for me to find opponents for classical games. Today was a stroke of luck because of the classical shield arena, so I took some time off work to play in it until my rating deviation got below 75, enough to show up in the high scores.

So right now it's 73.51, but it keeps slowly increasing. And it stresses me out because every time I check back, it's gone up a little bit, and it's so close to 75 that I know soon enough it'll go over 75 and I'll lose my top 50 trophy.

What's the formula for the increasing deviation? How much longer do I have before I need to go back to the pool and try to find classical games?

You need to play more games to lower it. The larger the sample size, the lower the deviation is.

I cannot remember when the deviation is effected by not playing for a certain amount of time, if it even is, but the only way to lower it is by playing more.