Congrats on the offer.  Though you have no legal obligation to stay after giving your resignation, two weeks is generally suggested as a matter of courtesy to the employer to transition any unfinished work to others.  Of course, if u are moving to a direct competitor, typically you will be asked to leave right away.  I would give two weeks notice, u don't want to burn any bridges, it's a small world, you may cross path again with your boss/coworkers.