That's entirely up to you.
The product is 5 mg/ml. We know that sublingually you are lucky to get absorption of 1/10, and that is from very slow dissolution of a lozenge between gum and cheek. Just putting liquid in the mouth for a short while would give less than this rate - probably much less.
Absorption from the topical products from B12 Oils has been measured at about 80%, so is very comparable with injection.
We don't really know what absorption would be from home-made topical stuff (ie liquid B12 plus a lotion) but it seems to be pretty good judging by potency compared with the B12 oil (This was my own experiment. I wanted to try quite high doses topically and it would have been quite expensive in the long term with the B12 oil product so I tried alternating comparable doses of the two products).
Typically, injections are usually from 1-5 mg/daily. This is a very high dose (comparable to at least 10-50 mg sublingual). I thought the home-made topical would be a bit less than this and tried up to 10 mg liquid plus lotion in divided doses. I certainly noticed it! Unfortunately continuing at this dose was too stimulating and I backed off. Still next time I decide to try big doses of B12 I'll use the Bluebonnet product again.