1. A computer readable program storage unit encoded with instructions that, when executed by a computer, perform a method for determining a time of beat sequence of the patient's heart, comprising: obtaining a time series of fiducial time markers for candidate heart beats; identifying valid heart beats from said candidate heart beats by subjecting a plurality of said candidate heart beats to at least one beat validity test, said at least one beat validity test comprising at least one interbeat interval test applied to a candidate heart beat interval derived from a candidate heart beat and at least one prior heart beat; accepting as valid heart beats the candidate heart beats that pass said at least one beat validity test, wherein a constraint defining said pass is modified after the most recent prior valid heart beat that is greater than a constraint modification time threshold; and performing at least one responsive action based upon at least one said valid heart beat, the responsive action selected from the group consisting of issuing a detection for an epileptic seizure event; delivering a neurostimulation therapy to the patient to treat an epileptic seizure event; warning at least one of a caregiver, the patient, or a physician; and logging said modified constraint to a memory.