Due to multiple factors, expect to potentially pay more when booking in August. For low rates, July can be a great choice for travel to Taichung. Flights to Taichung from Johor Bahru in July are about RM 1,250 on average during July, but can be found for as low as RM 925.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Johor Bahru to Taichung as you normally would.