We just returned from Orlando last night and made it onto Slime Time on Wednesday. It was so incredibly frustrating because I got so many different answers to my questions when I called various Universal numbers so I decided to post my experience here.
The banner at the studios says they will tape through May 24th. I would definitely advise calling them for exact taping information though.
Tickets are given out at Nickelodeon Studios only. The line starts to form when the park opens, but doesn't start to get long till 11:30 or 12:00. Kids must be at least 6 years old to get a seat in the audience and 9 to participate in the show. They pulled the first 30 kids out of the line to audition for the show. They were broken up into groups of 9-12 year olds and 12-15 year olds. These are the kids that will participate in games and such. I was in line at 11:20 and they already had more than 30 kids so if you want a chance to audition... line up EARLY.
There were two times for the show 3:30 and 4:30. We were in the first group and then they moved us out and the second group came in. We taped 8 segments and a promo for the Kids Choice Awards... our side did the one with Jess that is airing now.
If they tape outside, younger children can hang out around the barricades and still get shown on tv. Also, if people don't show up for the actual taping they will fill spots in the audience with kids waiting outside. If you really want to be in the audience and don't get tickets hang around when they are doing the tapings.
They will give a ticket to only one parent and however many children in a family. There were people who got in line with one child and then had the other parent get in line with another child... PLEASE don't do this... you are taking a seat away from another child who wants to be there just as much as your child. Only one person from your party has to be in line for most of the time... if you are close to the front and your kids want to audition they have to be in the line at 12:15. Everyone has to be in line at 12:45.
Rest your voice and prepare to scream and yell. They want constant noise for the couple of minutes they are on the air. I think this is why they let the parents in.

The hosts won't sign autographs or anything, so don't expect that to happen either.
I observed this routine for a couple of days, and this was my experience, so take it for what you want. I am sure I forgot many things in my exhaustion, so if you have any questions I would be happy to answer them if I can.