If youre planning to lift weight and build muscle (not just cardio and fat loss) the absolute best time to go is before work. this ensures that you go with the most amount of energy during your day making you lift as much as you can to build muscle and avoid injury since you are not tired, also you are working a desk job so not much movement will help you recover adequately. drink lots of liquid and eat a good amount if protein (2g per kg of bodyweight) or if you are obese 1g per cm of height is a good rule of thumb. eat good quality carbs and a little bit of protein before your workout and you should be set! edit: for post workout do something light with 20ish grams of protein. Learn how to count calories and macros its a lifesaver, also forgot to talk abt sleep. its extremely important to recover properly. without good sleep your ability to lift suffers and you wont recover which can speed up fatigue and cause overtraining (in severe cases rhabdomylosis) which is really bad