When it comes to meeting characters, in general, I have 2 pieces of advice.
1. Never go by the posted wait time, go by what the line looks like. I always look at the line and try to estimate how many groups there are. I assume 2 minutes per group, but expect larger groups to take longer. If the line looks short, the wait should be short. If the line looks long, the wait will be long. If the line is long, you will likely have to wait through a 5 minute break or 2 for the character(s) as well.
An example of why not to trust the posted wait. My girlfriend and I were at DHS Thursday. I checked the line for Olaf around 3:30. The outside queue was pretty full and the posted wait was 30 minutes. I could tell just by looking at the line that the wait would indeed be at least 30 minutes. I decided to pass and check back later.
After we watched the Star Wars stage show and The Little Mermaid, the app showed 20 minutes for Olaf. We went back, but the line didn’t look any shorter than it had been earlier. My girlfriend went to use the restroom. While she was gone, the posted wait dropped to 10 minutes for some reason, but the line hadn’t gotten any shorter. I had worn my button-up Olaf shirt this day specifically for the M&G. We weren’t planning to be at the park much longer, so I decided to just go ahead and get in line to meet him at 4:30. Despite the 10 minute posted wait, I knew I’d be waiting over a half hour. It ended up being 50 minutes.
2. M&Gs are always funner when the characters interact with you. Wear something that will get a reaction out of the character you’re meeting. The obvious choice would be to wear a shirt of the charter you’re meeting, but my favorite M&G I’ve had was when I wore a Donald Duck shirt while meeting Chip and Dale.
Here are my photos with Olaf. He loved my shirt, of course. He was pointing at the items on my shirt and then pointing them out in the backdrop.