If you're questioning the time of day, choose the warmest time of day to bathe the dog. Try to dry the excess water off and get the dog as dry as you can before putting it outside or letting it run around.
If you're concerned about how often you should bathe the dog, that will depend on how you're keeping the dog. Inside dogs do not need to be bathed as often as outside or inside/outside dogs. In general, you don't want to bathe them too often because you can easily dry out the skin, even using dog shampoo. Try once or twice a month, if you can't go longer.