Time here is a user end setting, so you can't set one for the board as such. You need to go to your User CP and in Edit Settings you can adjust it, so posts across the network appear in your time zone. Here is a chart covering the main timezones:
- Pacific Standard Time: GMT-8
- Mountain Time: GMT-7
- Central Standard Time: GMT-6
- Eastern Standard Time: GMT-5
- Santiago: GMT-4
- Buenos Aires: GMT-3
- London: GMT+0
- Paris: GMT+1
- Cape Town: GMT+2
- Moscow: GMT+3
- Bangkok: GMT+7
- Hong Kong - GMT+8
- Tokyo: GMT+9
- Sydney: GMT+10
- Auckland: GMT+12