Is walking after dinner actually better than walking at other times?

For blood sugar specifically, yes. A ten to fifteen minute walk starting within thirty minutes of eating measurably reduces the post-meal glucose rise, because working muscle takes up glucose without needing much insulin. The effect is largest after the biggest carbohydrate meal of the day, which for most Indian households is dinner. For general fitness the timing does not matter and total volume does. So if you can only walk once a day and you have blood sugar concerns, after dinner is the higher-value slot. If you do not, walk whenever you will actually do it.