JC:
If you are still going to take hwy 12 (which I do highly recommend) to 89 then down to Zion then you will literally drive right by Bryce. While Bryce is one of my favorites it is one you can get the general gist of by spending only a couple hours there. Go in to Sunrise Point, park, hike down at Sunrise Point back out at Sunset point or vice versa. It is only a couple miles at most. You will come up a couple hundred yards from your parking spot and you get the real feel for the park in just that one short hike. Even if you dont do the hike and just walk between those couple viewpoints it is worth the hour it will take and you will still get to Zion well before dark that day. I think Bryce to Zion is approx 100-120 miles ish. On the other hand if you dont take hwy 12 you can take I-70 to I-15 down to Zion in about 5 hours or so. However the scenrey starts out great on I-70 once past Green River and going up on the San Rafael Swell but once down the other side it gets less and less so until you hit 15 then it is well not much scenery until you turn off to go to Zion and even that is not great until you get there.