Done as I suggest, you can just slide the package along with the following one in contact. Only the few bees in the old container to deal with.
You don't say at what rate they are taking it. If it is slowish, then no bother - just change them. If they are beginning to brood and they require more, it will soon be time for 1:1 sugar solution. They would need to be flying for water if brooding on fondant.
Of course, you can use the other hole if you wish. I just use the one hole because insulating around the container is a cinch.
One or two more weeks before giving any of mine a knee-up. Or they might need a lot of feeding before the first flow, especially if the weather were bad.
I reckon feeding bees for early expansion is an art left to those with several colonies, or with a little experience of the potential problems, not really for the one colony apiarist in their first year, so just let your bees develop steadily at their pace. Dependent on how much space they have may be a limiting factor for their expansion.
RAB