Do not delay ones vowed or voluntary offering.
“When you make a vow……do not be slack to pay it” Devarim 23:22
One does not transgress this until three pilgrimage festivals (Pesach, Sukkot and Shavuot) have pass by for him.
Charity is also in the category of “vowed offerings “however regarding charity if a person delays he immediately violates this prohibition “do not be slack to pay it” since poor people are numerous.
If there are no poor people, there he can set the money aside until he finds a poor person.
If he stipulated that he would not give it until he found a poor man he does not need to set it aside.
This applies in all places at all times for men and women.