Two point seven minutes. However once you have added the 2 hour check-in time at N-u-L International airport and an average allowance of 46.3 minutes to collect your bags from the (ill-functioning) carousel at Hanley regional airport, it often works out quicker to utilise the number 47 bus.
Like you, I am somewhat bemused by the number of folks who want to know how long their flight time is. Its trivial stuff.