Oxymels are a lovely way to cut some of the acidity of vinegar preparations for sure. The honey also adds it’s own special blend of anti-oxidants, soothing, healing and anti-microbial qualities.
In terms of the garlic oxymel in particular, dosing and consumption would depend on the person and the situation.
I know that garlic can be hard on some folks digestive systems. By creating an oxymel, it can reduce the irritation, but if you have a hard time with vinegar as well, I would suggest just doing a garlic honey.
These can be taken daily if you are doing it for cardiovascular and antioxidant support, and could be added to salad dressing etc. to make it less irritating directly.
Or it can be taken acutely during a cold for example, where the dose would be increased a little bit.