Your bus gets in many miles away from the Park at 7:30 at night. Contact the AT Lodge about their MEGA deal, they'll pick you up, put you up for the night, and take you to the Ranger's cabin the next day. It's really a good deal.

Watch the snow melt here: http://www.neoc.com/webcam/twin-pine...am-camera1.php
and here: http://www.chesuncooklakehouse.com/webcam.html
and from the east: http://www.katahdincam.com/
Please don't call it 'the big K' or 'Mount Katahdin' - the name of the mountain is Katahdin, and the summit is Baxter Peak.
Share - the bus ride, the shuttle, the campsite - save $, make friends.
You're most likely not going to climb on May 15th. Here's my 'unofficial' list of opening dates over the last several years:

'11 Park is considering postponing May 15th opening.
'10 May 25th
'09 May 20th for both Hunt and Abol.
'08 May 29th (Park had canceled May 15th opening)
'07 May 31st
'06 May 18th (Abol May 15th)
'05 June 4th
'04 May 16th
'03 May 24th
'02 May 15th (Day hikers summited via Abol May 10th)
'01 prior to May 20th
'00 Memorial Day Weekend
'99 May 18th (per South Walker '99)

You want to book a lean-to for the night before and after your climb. Your gear stays dry, you can get a pre-tourist start in the AM, and you get to recover from the AT's hardest 10.2 miles around a campfire. The long hike out the next day to Hurd Brook Lean-to can be a slog with tired legs, so relax and get a well deserved good night's sleep.

Map: http://www.baxterstateparkauthority....mpgrnd-Map.gif
Tent sites 16 and 17 are roomy, plenty of space for two or three backpacking tents,
Lean-tos 1-3 are quiet walk-ins, lean-tos 4-8 are streamside and away from the parking area.
Buy a bundle of firewood or two at the Ranger's cabin. Cash only, you can also buy maps and guides.
Note: The AT has been relo'd to go straight across the tote road and behind Grassy Pond, a throw back to the route Earl Shaffer took.
Yes, you can start before 7 AM if the trail was open the day before.
Local radio station and weather: http://www.themountain949.com/
TALK WITH THE RANGER!