That depends. Cardio will decrease muscle mass only if done excessively. But if done in moderation, it helps improve muscle retention. Are you a lil' overweight? If so maintain you cardio but in moderation.

Some will tell you the anabolic window of opportunity is 30mins, some 1 hour and another 2 hours. Some articles on T-nation even say 24 hours. Just to be safe, within 1 hour. No worries. It also depends on your preworkout meal. If i had wheat bread and chicken preworkout, I'll still have protein inside my body so i won't really rush for postworkout.