I would say that would depend on the students record. If they skip a lot no... They get good grades and go almost everyday then yes. This choice should be given to students at the beginning of the year. All students should be able to until they start missing a lot of days or bad discipline.
I think that that all depends on the maturity level of the student. If they are grown up enough to take the responsibility to go off campus and then come back rather skip the rest of the day, then yes I think that would be a great idea. If, on the other hand, they are immature and can't be trusted to return to campus after lunch, then they should not be allowed this privilege.