We prove a time hierarchy theorem for the promise-BPTIME. This is considered to be a folklore problem and was thought to follow from the existence of complete problems or through direct diagonalization. We observe that neither argument carries through in some immediate way in the promise version. However, the hierarchy theorem can be proved by the standard delayed diagonalization for the nondeterministic time hierarchy theorem [Coo72, SFM78, Zak83], or, as it was observed by Rahul Santhanam, from the established BPTIME hierarchies with advice [Bar02, FS04, GST11, FST05, Per05, vMP07, San25].