Can't say for sure, but you could just phone Mt Seymour and ask them. It may be part of the seasonal operations.

I am not 100% sure ...

but I read that the Mount Seymour Parkway Seismic Upgrade work is underway for Bike Lanes Project (partnership with North Vancouver District, TransLink and the Province of BC). The second phase involves widening of the roadway between Seymour Boulevard and Riverside Drive to provide bike lanes in both directions.

I spoke on the phone with Ellen Fulton, who is the BC Parks employee responsible for Mt. Seymour Park (and incidentally is stationed at the park). The resort has an operating contract, and as a condition of that contract, while the resort is in operation, the resort is also responsible for salting and plowing the road. The resort (probably correctly) feels that they might therefore be liable for an accident that occurs on the road during the period for which they are responsible for salting and plowing, when that accident occurs from a failure to salt and plow. Because the resort does not salt and plow at night, or until 6:30 a.m., the resort elects to close the road, so no accidents for which they might be liable would occur.

I also asked the employee at the gate, and he mentioned that the road would be closed during the mornings this year until April 14, and that it had closed on November 1, which corresponds with the information I received  from BC Parks.

This might be old news to many, but apparently when the bottom gate is no longer closed in the morning, the gate in the parking lot near the overnight parking is instead closed from dawn to dusk. All of that makes me wonder if the resort might be happy with some sort of waiver in exchange for early access, but I doubt they'd be willing to accommodate me, given that I've been bothering them all morning with questions. Ha!

In any event, they let us through at 6:30 a.m., and we managed a few quick turns despite the road.