Suppose an organization spends 1⁄4 of its reserves every year, and earns a 5% return on those reserves. If I make a $1 donation, the org would increase its spending by $0.25 in year 1. In year 3 it would increase its spending by (0.75)*(1.05)*(0.25) = $0.20. Year 3 it would spend $0.16, Year 4 it would spend $0.12, etc. In the limit the full donation, plus accrued interest gets spent, even if it sits in a bank for a while. The timing would concern me only if I felt that money spent on nuclear security this year would be significantly more valuable than money spent in subsequent years.
Suppose an organization spends 1⁄4 of its reserves every year, and earns a 5% return on those reserves. If I make a $1 donation, the org would increase its spending by $0.25 in year 1. In year 3 it would increase its spending by (0.75)*(1.05)*(0.25) = $0.20. Year 3 it would spend $0.16, Year 4 it would spend $0.12, etc. In the limit the full donation, plus accrued interest gets spent, even if it sits in a bank for a while. The timing would concern me only if I felt that money spent on nuclear security this year would be significantly more valuable than money spent in subsequent years.