Wiktionary
double booked
a. (context idiomatic English) Of a single resource, reserved for two different users at the same time.
Usage examples of "double booked".
Maggie had been due to conduct a meeting of the Camden Town coven in one of the upstairs rooms tonight, but her secretary had muddled the dates and they had found themselves double booked with the Norman Wisdom Fan Club, so Arthur Bryant offered to buy them all drinks.