The styles (surface only inflation, oral inflation) reflect a range of thoughts on what the things are for, and when you should deploy them. If you are doing regularly diving from an anchored/moored boat, your ascent line is the anchor line/mooring line. The only reason to deploy one of these things in that situation is if you are in trouble, and need the boat to come get you.
If you are doing drift diving from a live (also drifting) boat, the SMB is going to be shot a time determined before the dive. Assuming the surface current and the bottom current are running the same rough direction, and there is no wind on the surface, the captain might want you to shoot the SMB when you start your descent.
If there are a number of separate groups you may only shoot it when you hit your safety stop or maybe only when you have 3 minutes left on your safety stop. If you are shooting it in those circumstances, you just won't get a whole lot of air in it. That's when the blow into the bottom of the bag inflation type can be good because you can usually hit the bag with your bubbles from the safety stop to get some more air into it.
Or you might only deploy if the boat is not right there, and they do not seem to see you.
If the underwater current, and surface current don't match, or there is a prevailing wind blowing against the current, you may shoot the buoy once you hit start ascent, hit max depth, etc. etc. You have to know what the captain wants, and know what the captain is taking a shot buoy to mean.
When I was leading divers, the captains I dove with knew that if I shot the buoy at the beginning of the dive, I was letting him know that there were strong currents, and the dive had just become a drift dive. Of course this was something that the captain of the boat and I would have discussed beforehand.
Summing up, there is no set way to inflate an SMB. There is no set time to deploy an SMB. There is also no way to know what the appearance of the buoy at the surface means to the captain. Local conditions, and local standards, determine everything. ANd then the captain makes the final determination.