tbh through the summer months it should last at least 4-6 months i reckon...if you add a couple of layers of wax on top too then that will prolong it some more

i have used Duragloss 111 clear coat polish (which is more of a sealant strangely) followed by a couple of layers of poorboys natty blue wax on the girlfriends mini, and it's still shining now a few months later ( only gets washed once a fortnight too tbh )

there are better combinations out there though dependant on the colour

ps...you need to also make sure you use good quality wash mitts (rather than sponges) and also dry with a waffle weave drying towel (rather than a chamois)

hope this helps