Doing some napkin math, if you're capping the pretax contributions now, 16 paychecks in, you're contributing a little over $1000 per paycheck. So $20 is just under 2% of that contribution. Since no one has a crystal ball to say how the markets will perform, I'm going to estimate that during the remainder of the year your money will grow another 7% * 4 / 12 or 2.3%. In that projection, even if you put all the money your would contribute for the rest of the year at once (which you aren't since you're contributing a little each paycheck), paying to rollover after every paycheck is going to kill your earnings. I would keep it simple and just wait until the end of the year to do it all at once.
I believe rollover money still has to go through the 5 year seasoning before it can be withdrawn penalty free.
Do you have an option do convert after-tax contributions to Roth 401K money? I don't know if you have good investment options in your plan, but it may get you out of the $20 fee.
Edit: bad math