If someone had a sum of money to invest, would your advice be to invest it all over the next 6 months, or to spread it out over a year?

(this is not for myself btw, but someone asked me about this and I said I know a place where people might have some good input)

I know this isn't a simple question and largely speculation. I suggested maybe 3/4 over the next 6 months then the last 1/4 over another 6.