Open JSON log & type the following to convert all timestamps:
%s/"timestamp":\s*\zs\(\d\+\)\ze\./\=(str2nr(submatch(1)) - (7 * 60 * 60))/g
%s/"timestamp":\s*\zs\(\d\+\)\ze\./\=(str2nr(submatch(1)) + (8 * 60 * 60))/g
%s/"timestamp":\s*\zs\(\d\{10}\.\d*\ze,\)/\=strftime('"%c"', str2nr(submatch(1)) - (7 * 60 * 60))/g
%s/"timestamp":\s*\zs\(\d\+\)\ze\./\=strftime("%Hhrs%Mmnts", submatch(1))/g
Usage: Use str2nr(submatch(1)) - (7 * 60 * 60) as the second argument to strftime()
from datetime import datetime
import pytz
datetime.fromtimestamp(1350663248, tz= pytz.timezone('America/New_York'))
datetime.datetime(2012, 10, 19, 12, 14, 8, tzinfo=<DstTzInfo 'America/New_York' EDT-1 day, 20:00:00 DST>)