you could try and finish them hotter, up to about 275F
you could also wrap the butts in foil and return them to the cooker ... lot's of folks do it ... I'd rather not but it will speed things up
one more thing ... when you do remove them from the cooker, wrap them in foil and let them rest for at least an hour if possible
you need to keep them over 140F while resting, many use an old cooler and some blankets
I was wondering when you posted if you were gonna be a little short on time
if I want to remove the butts by 4pm, I start them around 8pm or 9pm (which turns into 9pm - 10pm) ... my last ones were done at 2pm which was perfect, a couple of hours rest before pulling the meat