The 7:07am train you KNOW will be there at 8:37, traffic or no traffic.

According to my check of the schedule, the limo bus leaves the Park Hyatt at 7:05, not 7:20. If you want a more frequent schedule, you'd have to go to Shinjuku station.

Personally, with this minor difference, I wouldn't even be asking about the traffic (which obviously can vary), I'd just take the train.