which is best day and what time is the best for emissions test?

MVA SAYS THURS+FRis are the Least Busiest Days. You can LooK on www.MVA.MaryLand.Gov for ReaL•TiMe WaiTs

Thursdays and fridays between 8am - 5pm. If your vehicle is 2005 or newer, you can use the kiosk 24/7.

I don't know, how can I do that self emissions, what's the process?

If it busy do the self emissions I was in and out in 5 minutes