Parametrize the "True for x minutes" parameter in event frame analysis

It would be nice if we could reference an attribute or analysis variable to provide the value for the "True for 'x' minutes" parameter, rather than having to hard-code this value.

This would be especially helpful in cases where we have numerous elements generated from a common template that includes an event frame analysis, but we don't want every element's event frame analysis to use the same "True for" parameter.