In cases where meetings are back to back, it can be handy to have things start at the 5 after. This helps folks who may be late, and also helps give a breathing space between meetings. The alternative is to do a 25 minute meeting starting on the 00 or 30 mark, but many meetings run long; the 5 minute buffer also gives room for those. This would mean all times are either :05 or :35, and meetings become 25 or 55 minutes.