A lot of people are asking what time they need to get in line for panels. Here's my most honest answer: I don't know. It's very hard to predict these things.
For instance, for years Hall H had a line days before the Con. But once Twilight went away, so did that trend; last year, the line for Thursday was quite minimal until Thursday dawn.
You can read my tips on lines from last year. Most importantly, if you're new, realize you'll have to wait in line to get your badge, which eliminates the possibility of getting in line early for the big rooms that day. (This is a bitter reality for people with one single day badge, which is why I wish CCI would let everyone pick up their badges in advance at satellite locations.) Also, always ask what line you're standing in unless it's supremely obvious. It's easier than you think to spend an hour in the wrong line.
Also - decide in advance if it's really worth it to spend hours and hours in line, then more hours sitting through panels that bore you stiff, to see a 50 minute panel of your favorite show. (Often from the back of the room, where you watch it on a screen.) A lot of times the panel goes like this - the moderator warms up the crowd for a bit, the stars emerge, they give a few semi-canned responses and banter with each other, then there's some footage, then Q&A in which the stars answer 1 or 2 questions each. And then it's over. Inevitably a shaky recording of the panel shows up on YouTube (or you can see it in the replay room) and then the footage is released to the public. In the meantime, you've missed out on a ton of other panels, and you're often too tired and hungry to do anything but eat a meal and collapse.
Only you know how zealous you are about seeing your dream panel and only you can calculate if it's worth it. I'm a cynical attendee who's been going since 2001 and I'm mostly over it. But I know some of you live for your big room experiences and will put up with any wait imaginable.
Hall H, Ballroom 20 and Indigo Ballroom
I know most of you are focused on Hall H and Ballroom 20. My estimation is that Thursday's Hall H line won't be that brutal (of course, my "not that brutal" could be your "horrible") and there will be a decent flow in and out of the room. Even though I abandoned all Hall H doings years ago, I may even try to get into Penny Dreadful Thursday. For Friday and Saturday, I think Hall H will have overnight lines and that a sizeable number of attendees will stay in the rooms all day. Sunday I think will have a line post-midnight but not as bad as Friday/Saturday. Hopefully the new color-coded sections will help discourage people from wasting fruitless hours in line.
Ballroom 20 is harder to predict. Often there will be a rush of people in the dead of the night who camp for it, then the first batch gets it and afterward it becomes hit or miss, where even a 90 minute wait can get you in. The most major exception to this is True Blood. The line for this is just appalling. A few years ago, there was a line where over 12,000 people waited, many overnight, and only 5K got into the room. Since then I think it's slightly better in that a lot of people have just given up on the idea and still others are just sick of the show. But will there still be a horrific line for it? Yes.
Indigo Ballroom is getting right up there in terms of attractiveness, so don't underestimate your line time here. Animation Friday is popular, John Barrowman, Felicia Day and the Nerdist panel will also pack them in. Just because it's technically offsite doesn't do much to reduce the line factor.
Other panels: my best advice is to keep an eye on the situation, if you're meandering around the convention center. Check in the morning, check 2 hours later, etc. I think most of us know when we're interested in a minor panel and when we're drawn to something extremely popular.
And on that note, don't hesitate to help out your fellow attendees. One thing that's helpful is posting line statuses on Twitter. If you see a line is getting really long, say so. It alerts people and helps them prioritize where they need to be. The reverse is also true; it's a bit galling when you get in line very early and then realize the people who slept in and showed up 4 hours later also got into the panel and claimed a good seat. So if a line doesn't seem too terrible, post that also. Experienced attendees will give markers when reporting where a line reaches to, rather than just saying something vague like "epic line" so do that if you can.
I know I'll still get emails asking for specific times to join a line. I wish I could be more helpful. But my best advice is to think in advance about how much time you're willing to devote, then monitor the situation the day of. Good luck.