Now I get and I can't advise you to always give yourself that chance of doing the push up every morning or every evening because of the nature of your work, if you don't it will affect you badly and you might even fall sick. But which ever way you feel you can get at least 50 push up you can do it. Is not easy to do the kind of work you do and also add it up with the push up, some persons can and when your body starts giving you pains I think is best to take things easy, early morning you can do the push up and skip the next day depending on how busy you'd be at work.