When I did the Beast from the East the Yeovil -> Waltham Abbey leg was raining lots, I followed a bent rider off course and ended up walking through deep slippy mud up a steep unmade road, the road grime was really bad, etc.
The chain was due a lube before I started, but I hadn't logged my mileage that week so hadn't realised.
The ride was 390 miles.
I rode again on the Bank Holiday Monday (short trips to the shops etc) and then commuted daily tue to friday. On the way home from work that friday I heard a faint squeak from the chain, which reminded me that I hadn't lubed it still. I'd ridden about 550 miles on one application of White Lightening. (Compare that to the 80 miles max out of WD40)