Hours, yes, although if you use years for Ln then Le will be years also. Note that if you just put V at just 20% more than Vn in that equation, it reduces the life expectancy to about 23%. A sobering thought!
If you put caps in series to increase voltage handling, you generally need resistors in parallel with each cap (or pair in this case) to ensure that the voltage is shared equally. Like a voltage divider with the centre joined to the junction between the caps. I'm not sure how that would work out in this instance though; possibly not well.