After logging in your Wyndham Account, there is a status match website (https://help.wyndhamrewards.com/s/status-match?language=de) where there is a list of accepted other hotel programmes and how they match to Wyndham Rewards. Using this website got matched on same day from Best Western Rewards Diamond Select to Wyndham Rewards Diamond. According the status match website there is a table how many stays have to completed within 90 days to maintain new status.