Good on you for waiting for the right time for you to get bees.
I don’t know how much you know so I will make suggestions pretty basic and detailed, I’m not trying to be patronising 🙂
Don’t be shy to look at your bees in nice warm sunny weather, swarm season is upon us and checking them every 7-10 days is not excessive.
Check them too infrequently and they can develop Queen cells and swarm on you.
There are a few exceptions to this rule, the main one being you don’t want to be in the hive when you have a virgin queen running around as they can be quite flighty and may fly away and not return leaving the hive queenless.
You also don’t want to disturb them too early, or too late in the day, or when the weather feels changeable. This can make them quite grumpy.
Use smoke and be as gentle as possible, if your squashing bees they won’t be happy.
Spring is the perfect time to get familiar with your bees and learn what normal looks like.
The main things you want to check for are that you have honey/nectar, pollen, and eggs, if you have eggs then you should have a queen.
And that your bees have room to expand.
It sounds as though it is possible that your hive may have swarmed, or that your queen may have superseded and could have been on a mating flight.
You will need to establish what has happened.
Open the hive, check for eggs. If you see eggs your probably good and there is a mated Queen, no need to worry if that’s the case, have a look around and see if you can find her, she’s usually towards the centre of the colony near fresh eggs.
If you don’t have eggs you may be between queens, you want to see if you have small grubs(larvae) and uncapped brood, that will tell you how long she’s been gone.
Then you will want to look for cells, if any of the cells you find are hatched then you likely have a virgin or maybe even more than one, if there are plenty of bees and young grubs then I would carefully close it up and check it again in 2 weeks to see if there are eggs and therefore a mated Queen.
If there is no uncapped brood and you suspect there is a virgin (you find a hatched cell) then check again in week. It’s likely if there is no uncapped brood that your new queen may have mated but not be laying just yet, next time you look only look for eggs and if there are none close it and check again in another week.
If you don’t have a new queen laying in about a month you will need to find a cell or another queen from somewhere else.
Remember that a DECA holder is only to inspect for disease(AFB) and sign you off, the day to day running of the hive and health for the most part is up to you and you will need to learn and be confident keeping your bees yourself.
This is a great place to come for help and advice, most people here will be able to offer you a lot of help just from a couple of photos.
We all started knowing very little and the best way to learn is to look at your bees, watch their behaviour and inspect their brood even if your not too sure what your looking at for a start.
Ok, so I watched your videos.
It is hard to say what is going on from the outside of the hive, you will definitely need to take a look ASAP.
It looks good and strong from the outside.
Where you have your hive placed looks like a good hot spot.
Is it on a solid base?
I would remove your entrance reducer to give the bees more room to get in and out and make it easier to ventilate their hive.