1) AFAIK, there are no public heliports for people other than those who are surrounded by large guys who wear "earpieces".

2) Even though you would think that I-66 and the IAD connector road would be lightly traversed that time of night, the Silver Line construction can lead to significant delays and closures.

3) Getting there also depends on where you are going to be within DC. If you're on the west end of DC, you can probably get to IAD in good conditions in 35 minutes. If you're over by the Capitol, Penn Quarter, or even Metro Center, you're going to be delayed by an additional 10 minutes.

4) I also put your odds of success at 40-45%

5) I agree with Often1's suggestions. I would add 1) PREPAY the sedan or put it on account, and 2) waive a $50 or $100 in front of the driver as a bonus. Regardless of how fast he goes on I-66, he will HAVE to SLOW down on the IAD connector road as MWAA police have been in high ticketing mode on that road (all needed to pay down the cost of the Silver Line).