Does anyone know if the Baht buses still run regularly from the Dolphin Roundabout to the bus station?

Yes, they do (at irregular intervals)....

Yes.  They wait at the front of the market.

An issue can arise with wating.  They may wait until the bus is full which can take some minutes.

Offer the driver 100 b if you want to go immediately.

The later in the day the more difficult it is to get one.

One of the things about living near a Thai neighbour that owns a baht bus is getting the whole family into town for 100 baht when he goes to work early in the morning. Sure beats life and limb running the train crossing on taxi bike

2 hours ago, champers said:

The later in the day the more difficult it is to get one.

In my case about 7 in the morning.

11 hours ago, possum1931 said:

In my case about 7 in the morning.

That should be fine, unless something has very recently changed, which I doubt.