slack and international flights

So, I'm sorting out my final detailed plans for getting to and from Japan, which brings up the always tricky question of how much time to allow. Heathrow's website these days says to allow three hours for checkin for long haul flights, which I'm sure is an hour more than last time. And I'm planning to get to Heathrow via the RailAir bus -- anybody know how close to its timetable the coaches run on a Monday morning? The timetable gives me the following choices, for a departure time of 14:00:

• Leave Reading 9:45 (arr 10:30) (the 'extra padding' option)
• Leave 10:05 (arr 10:50) (the 'I trust the bus timetable' option)
• Leave 10:25 (arr 11:10) (the 'I don't believe Heathrow about the 3 hours thing' option)

Recommendations?

(The whole thing is shaping up to be about 27 hours door to door; the return journey will be pushing 30 hours.)

mamonaku ichibansen kara...

Found recordings of Japanese station train-about-to-depart jingles on Youtube (via nosword); very evocative if you've spent much time on JR trains in the past... This short TV item about them is also interesting if you're the person who reads my LJ who understands Japanese :-)