Saw this info on another site;

Tentative Schedule for 2010 Yellowstone National Park Road Construction Projects (Subject to Change!)

NORRIS - MADISON: Gibbon Canyon

April 16 (8:00 am) ? May 28 (noon)
Road open with up to 30-minute delays.
Road CLOSED nightly 10:00 PM to 8:00 AM.

May 28 (noon) - June 1 (8:00 am)
Road open with no delays for the Memorial Day holiday.

June 1 (8:00 am) - July 3 (8:00 am):
Road open with up to 30-minute delays.
Road CLOSED nightly 10:00 PM to 8:00 AM.

July 3 (8:00 am) - July 5 (8:00am):
Road open with no delays for the Independence Day holiday.

July 5 (8:00 am) - September 1 (8:00 am):
Road open with up to 30-minute delays.
Road CLOSED nightly 10:00 PM to 8:00 AM.

September 1 (8:00 am) - October 20:
Road open with up to 30-minute delays.


EAST Entrance Road: SYLVAN PASS (Cody, WY to YNP)
May 15 - October 14 -
Up to 30-minute delays are possible
(This project entails reclaiming the pass, repairing
guardrail, and is a couple miles in length)


BEARTOOTH HIGHWAY (US 212):
Clay Butte Lookout Over Beartooth to Montana State Line

May 15 - October 14 - up to 30-minute delays
are possible. Nighttime closures possible.
No holiday closures.