One day, Chang-sha Ching-tsen (d. 868), one of the well-known Chinese Ch'an masters, wandered in the mountain. When he was back just at the gate of the temple, the head monk asked him:
-Where have you been, Sir?
You can sit at some time in the early morning if your working schedule allows you to do so. In the early morning it is often less noisy than other times during the day and the atmosphere is still more pure than later in the day or in the evening.
You may sit in the evening about 9:00 P.M. or later. It would be better if you start to sit about two hours after your meal because if your stomach is still full it will be not good for sitting. What has just been said is for a beginner, and if your are an enthusiast practitioner, whatever time would be good for you.