Once he's completely weaned of bfs, you do need to still make sure he's getting enough calcium.
Usually this is with 1-2 drinks of cows milk/day (so giving them at snack time like you said above would be absolutely fine
there's no "set" timing for this and Los may prefer it at different times ).
However, some Los don't get on with drinking lots of cows milk, and there are lots of other sources to get the nutrients from. (Hopefully some one more knowledgeable than me about that will be along to give some examples! But I know it includes things like yoghurt and cheese, obviously, but also some fish (sardines? Pilchards?) and broccoli, for example). Your LO might also have milk with cereal, for example, which would also count.