Question : How long do most people visit Siem Reap?
Answer : Of course you're not most people, but if you were, you'd stay roughly two weeks.
Question : Can you cut down on flight costs by changing the day of the week you travel to Siem Reap?
Answer : The cheapest day to fly in March is Saturday. Having flexibility in your travel plans means you can save more, so be sure to plan ahead when possible.