If it’s just a walk I go soon after tidying the kitchen, putting my dog on his leash and out the door. If I was doing a more demanding exercise, one that increases my heart rate and puts my body under stress then I wait an hour after eating.
@poppy659 there are no rules, only what suits you, your body and your lifestyle. As long as your bg is kept at a level you are OK with, it doesn't matter how you get it there.
Yes some find a walk after a meal helps their bg reduce more quickly than not walking. Others may find it makes no difference.
Your meter and your bg will be your best guide