This is a broad example of Russian online dating scams.
The period from first contact to first cash request could be a few days or a few months but regardless how long you've "known" the person, a request for money is a scam.
Scammers operate from countries with low per capita income and even if a scam takes months to pay out it is worthwhile for them, even for just a few hundred dollars.
Scammers use services like Western Union because it is all but impossible to track the recipient of the money which can be picked up anywhere in the world.
A scammer could be a man or woman operating solo, posing as an attractive young lady, or part of an organized scamming operation.