We get charged airborne time (T/O and Landing) + ten minutes for taxy. This sometimes works in our favour if we are taxying and holding for 20 minutes but sometimes it doesn’t
I would be surprised if your total taxi time (remembering to include taxi in) is much less than 10 minutes, I can be pretty quick but getting airborne in under 5 mins needs starting pretty close to the runway threshold, and at most airfields that will mean a longer taxi in, most people do well to taxi out, do the checks and get in the air in under 10 mins, so adding 15 mins to airborne would not be unfair - though of course this time does not count towards engine hours!