Yes. The gate opens 30 minutes before scheduled park opening which allows you onto Main Street to shop and meet characters. Mickey + Minnie will always be greeting and some of their friends may be greeting (Chip + Dale, Goofy, Pluto, Donald, Daisy). Duffy and friends may also be greeting before official park opening.
Lines can fluctuate depending on crowd levels. Mickey + Minnie will typically be around 90 minutes while other characters will be more like 20 minutes. Most characters are on 30 minute rotations so you should try to arrive around the time their set begins because CMs will cut the line once a certain number of people is reached. Due to the low crowds these days, sometimes the Adventureland characters roam instead of stand for meet + greet.
