Determining sub-period probability from overlapping temporal probabilities

#1
Hi.

If the probability of an event (e.g. thunder) occurring in the 12 hours spanning 5 am to 5 pm is some value ...and...
the probability of the same event (e.g. thunder) occurring in the 12 hours spanning 11 am to 11 pm is another value...
can the probability of an event occurring in the 6 overlapping hours (11 am to 5 pm) be determined?

The degree of dependence/independence between the two events is unknown.

Thank you.