Every track and their officials will be different. I can't speak for a BPG race as I have never raced at one of their events.
Typically during the week of the GS Nationals in Bowling Green, weather permitting, there are times for Test and Tune. With good weather, you could easily make 5-6 runs with plenty of cool down between passes. For Heads Up Class racing and for Bracket class racing, they are strict about rules. With regards to how many 10 second passes they will allow you to make during Test and Tune, you might get away with one or two 10 seconds passes before being asked to slow it down or else. Maybe more, it really depends on the track officials. Especially when there are tons of Turbo Buicks making test passes doing the exact same thing. Your question has been the age old question every Turbo Buick owner has asked at some point about Bowling Green and it has been hotly debated over the years. But let's put this into perspective for a minute. You've spent a boat load of money at this point on the car. How much is your safety worth to run a 10 second pass? I mean, these aren't new cars and track prep at Bowling Green during the week, is minimal at best. My advice is, do it right the first time, get the roll bar. Especially if you intend on racing the car at other tracks in the future, anywhere in the 10's. Peace of mind is worth a ton when it comes to these cars. I speak from experience on this as I ran my first "86 T-Type in the 10's for about five years, before I finally broke down and installed a roll bar. It was tough doing it to the car, but it was needed for safety and for my peace of mind. And with the car going faster and faster, it just did not make sense not having one. A lot of things can happen in 10 seconds. Over the years, there have been a few wrecks at Bowling Green where the roll cage saved the driver. Odel's incident a few years back at the Nationals is a perfect example. Given that was an 8 second car, but it proves the point. It was horrible seeing that wreck on such a nice car, but the cage did it's job and he's alive and well today. Heck, I've seen 12 seconds cars loose it on pass and roll over. Also, you can have a roll bar tastefully done and well hidden with these cars and still have a useable back seat. And the benefits that a roll bar gives for stiffening of the chassis are another plus.
If your plans call for 10's, my advice would be to get the roll bar. Your car and your conscience will thank you for it.
Just my O2's worth.
Patrick