``Michelle was born yesterday'' is a typical indeterminate event. An indeterminate event is composed of an event (e.g., ``Michelle was born'') and some indeterminate temporal information (e.g., ``yesterday'').
Note that an event with noncontiguous temporally-indeterminate information, such as ``Jack was killed on a Friday night in 1990,'' is not an indeterminate event since the times when the event might have occurred are non-contiguous. The incomplete temporal information could be more substantial. For instance, an indeterminate event could have an associated probability mass function which gives the probability that the event occurred during each chronon on a time-line.
Currently, there is no name used in the literature to describe the incomplete temporal information associated with an event. The modifier ``incomplete'' is too vague (-E9), while ``fuzzy'' has unwanted connotations (i.e., with fuzzy sets) (-E9). ``Indeterminate'' is more general than ``imprecise;'' imprecise commonly refers to measurements, but imprecise clock measurements are only one source of indeterminate events.