30 day survivorship clauses in wills

[cartoonheart]

why are they set out 30 days? is this just the norm? or can it be sometimes longer or shorter?

(i'm in the uk)

(incidentally, wasn't meaning to be a pain in the bum, mumblechum1... and do appreciate all previous answers)

(also, not a lawyer - so perhaps am not good at getting my head around these things)

It's partly to prevent having 2 lots of executorship expenses and partly to speed things up so that the distribution of one estate isn't slowed down because it's entangled in that of the other.

And the costs of waiting around for 6 months which i still think would be legal mean its better to get it done in 28 or 30 days and that 28 or 30 days would be still considered a useful period in case of a car crash or similar

.

It doesn't mean that the first estate is finalised within 28 days, just that you have to survive the deceased for 28 days before you become entitled to inherit (acquire a vested interest is the technical term). It's not "illegal" to wait for 6 months, if that's what you want, but it does mean the beneficiary cannot receive any money from the estate during that period. Which could present difficulties.
It usually takes a few months to deal with an estate but can take years, it depends on the assets in the estate. If, for example, you have to sell a house, you will have to wait until you can find a buyer, which can take a while. There is no fixed time period.