Too much current is being drawn - either just too much in which case it takes 5 minutes to melt -or- much too much after an interval of five minutes.
Either way it will be good to discover which circuit the fuse is in else troubleshooting will be difficult.
An auto electrician may help but the Haynes Car Maintenance Manuals have comprehensive wiring diagrams - Amazon sell them and some libraries keep a few copies.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.