Is the damson and sugar something you have already made and fermented? if so this will be more akin to a wine? Traditionally damson, plum, sloes etc are more of an infusion where the spirit is allowed to soak into the whole fruit over time, there would be no more fermentation taking place once spirits are added as there abv would kill of any yeast.
I would be inclined to mix a drop up to see if you can strike a balance and go from there, i don't think you would see any benefit from letting it mix and mature, wine will mature in the bottle but spirits don't tend to improve at all. At a year old your damson will be in already decent shape, i would look to forage some new damsons (or sloes) and let them infuse into your gin which would be ready for xmas.
