Evening Graduation - even worth trying?

My son is graduating next week, and I'm flying to be there and wanted to photograph him getting his diploma. It's going to be outdoors at a football field, and it'll be starting at 8:30pm. Sunset is at 9:27pm. There are 538 kids in his graduating class, and our last name starts with 'S', so I expect it'll be at least 9:30 by the time he is called. I originally thought the ceremony was going to start at 6:30, which would have left me with enough light, I think.

I'm bringing my Tamron 70-300 f/4-5.6 VC, (and some others but shorted FL for other things) and I'm thinking now I won't have enough light. I figure at the closest, I'll be 100ft away, unless they'll let me get close to the stage. I was also going to have a 1.4xTC, but now I figure that will be pointless.

Camera is a 50D, and high ISO is not it's strong point. I do have triggers, but I doubt I'd be allowed (or want) to leave a triggered flash at the stage.

How can I capture this once-in-a-lifetime moment? Or should I skip the attempt, and just watch?

I'd bring a 135L, try to get closer, and hope I can crop a nice result from it.

There will be stadium lighting and the Tammy has VC. You should be able to pull out shots at 1/250 or 1/200 f/5.6 and ISO 3200. Yes, there will be noise, but it is what it is. You can also try using a 580/600EX flash with a Better Beamer flash extender if flash photography is permitted; that might give you enough light at 100' to shoot at lower ISO.

Short of renting a 300/2.8 I think it's the best you can do.

The closest I have to a 135L is the 85/1.8, which really isn't close, but I do have a TC (1.4x and 2x).

Seems like they timed it poorly. Maybe there will be field lights? If there's another group of hired photographers, you could always purchase something from them. I know my parents did for my younger brother. Poor light though with the outside sun.

This spring I was able to get nice photos for my other graduating sibling. I find graduations incredibly boring. I didn't even go to my college one, and I would have skipped my high school, but I think they set a high dollar penalty, so I just pushed through.

For occasions like this, be a parent with a camera and take a photo. Don't be a photographer who is a parent and look at all the technicality of the shot. Capture the memory as the parent. Just my 2 cents.

Is there a hired event photographer? I would get his card and ordering info. You would have a better pic of this important event.

Well, I think it was a success! We were seated 3/4 of the way up the bleachers, just to the (camera) right of the stage. Lighting was decent, but I would have liked a little more. Used my Tamron 70-300mm with no TC, at 300mm. Exif should be attached, but it was at ISO 1600, 1/100, f/5.6. The images were noisy, but Nik DFine cleaned it up pretty well.

Still have to figure out the best crop, but here's the diploma handoff -

Glad you got it. Surely came out better than expected.

Don't you hate it when the pro's flash gets in your shot?
Kidding aside, very nice capture. Congrats.