Manual wound watches
Your mechanical manually wound watch has a mainspring that has been designed to last for a full 30 hours between each winding. You should rewind your watch every morning at about the same time. This will give the watch the mechanical energy required to power the movement smoothly for the next twenty-four hour period.
The reason that we suggest winding your watch in the morning is simple. The watch movement has to work a little harder during the day, as it compensates for the activity of your arm. A fully wound mainspring will give a more constant flow of energy to the movement. Conversely, the watch has to work a little less hard when it is static - at night.