The term cadence is often used for the period (or frequency) of periodic observations. It may (incidentally) roughly equal the time between observations, e.g., when a 5-second observation is made every 30 minutes, or the exposure time of individual "snapshots", in the case where something is being observed continuously, but CCD "counts" are stored periodically. This use of the term is common when transients are being searched for or observed, such as transits, gravitational microlensing, or radial velocity indications.
The term mean cadence is often used in describing surveys that are loosely periodic, which is common for long-term (days/weeks/months) light curve observation, such as those of supernovae: the survey's mean cadence might well be some number of days. Over such a long term, telescope availability and weather often make exact periodicity impractical.