Lots of time. BKK does not have the most efficient layout (it is actually one of the worst new airports in asia in respect of walking distances).
When arriving just look for signs for the transfer counters - there are two areas, so check on which side of the airport the CX counter is. It will take you between 5 and 15 min to get there.
After getting your CX BP go upstairs to the gate. This should take you also not more than 10 min or so.