I did this last year on a Saturday morning. I took the 8am DCA-LGA flight up and the 10am LGA-DCA flight back. No problems whatever. In LGA they have a Shuttle check in area inside security- so you do not have to go outside-- Just make sure when you deplane in LGA you go out the plane door and do not use the stairs out the back of the plane. This will make it easier to get to the check in area.--