So I seem to try to keep my mind busy and all that WILD stuff, but when I’m just tired of just staring at color lights going and fading, I open my eyes and realize it’s passed an hour and a half since I went bed.
I know it might take some time, but for God’s sake, it’s been 90 mins and nothing!
Try relaxing your body more before attempting (you can find a lot of pretty good techs around here, or by googling), it helps in falling asleep faster. Seeing as you’re already on your way to HI, that should pretty much be everything else needed for you. Always remember that falling asleep is a required part of any WILD 
At what time are you trying to WILD? If you’re trying to WILD at night, when you first go to bed, this could be the problem. Using WBTB greatly increases your chances of succeeding with WILDing. If you are using WBTB, and you’re still having trouble, then try to focus on Hypnagogic Images rather than the lights on your eyelids. To do this, you simply imagine that you are looking at your thoughts through a “third eye” on your forehead. Hope this helps. 
I run into this problem too, I’m too excited and can lose hours to watching HI. I agree with Vampirism45, make sure that you’re doing your WILD after a WBTB.
I find that if I’ve spent over 45min, I likely won’t succeed. So, I try something different. Get up, wash my face, stretch, and then go back to bed. Otherwise, hours can slip away with no dreams at all.
It’s a very difficult balance, to watch your HI impartially until you can “jump in”. If you’re watching too intently, you can keep youself from falling asleep, and you need to sleep to LD. And, if you let yourself drift too much, you get a regular ND.
Good luck!
WBTB or not, I can’t seem to fall asleep laying on my back at all…I just get REALLY REALLY tired - and falling asleep is necessary to WILD. maybe this is your problem.
Set a time limit on your attempt to WILD, if it hasn’t happened in 30 min, try again tomorrow. That way you don’t lose precious sleep. I started doing that. I know it’s possible to do it within min so 30 min seems reasonable.
I thought these were “thought images” not HI. Thought images are like the images we imagine throughout the day only clearer, whereas HI are like images right on the inside of the eyelids, which I have seen before, but rarely and don’t require looking in only looking out. This is how I always understood it anyway.
The colours we see when we close our eyes are called phosphenes:
en.wikipedia.org/wiki/Phosphene
Random colors, swirling miasma, no real images. (Unless you consider looking at clouds and guessing what they look like as images).
HI, on the other hand, can be sights, sounds or entire thoughts that occur just before sleep. These are more like our day dream imaginings, but with no control and no order. Much shorter, no story. Can you picture in your mind a shiny red ball with a blue star on it? That’s not on your eyelids, that’s more like an HI. But, with HI, we have no control, they’re very random.
But, in time, these HI images can coalesce into a dream.