Is it okay for my husband to go the gym an night?

He usually goes in the evenings before dinner but his parents are visiting and so now he comes early in te evenings to have dinner with them while they are here for a month so he goes to the gym after dinner and after we put the kids (3 and 1 to bed) so it ends up being around 9:00-10:30 ish. Is this too late? Am I worrying about nothing? He never used to go the the gym around this time but he is stressed with work and the workout helps him. I am just not comfortable with it being so late. >Am I being paranoid?