what time the Hong Kong metro from Lamtin to central operate in the morning?

You must refer to Lam Tin Station, right?
About the transportation, there is no direct metro. You need to take Kwun Tong Line to Yau Tong Station and Tsueng Kwan O Line to North Point Station. Then take Island Line to Central Station. The operating hours of Kwun Tong Line are from 06:07 to 00:22.
After arriving at Central Station, walk to HK Station and take Airport Express. The schedules are from 05:50 to 00:48.