Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
inter-vallo, āre, v. a. [vallum], to take or assume at intervals (post-class.): intervallando potestates assiduas, Amm. 27, 11.
Hence, intervallātus, a, um, P. a., separated, having intervals: febris, intermittent fever, Gell. 1, 12: intervallato brevi tempore, after a short time, Amm. 26, 1, 3.