They would not think twice about letting you go if they had a business need to do so. There would be no "Oh, is this time good for his wants/needs/goals?" It would be "Here's your pink slip, have a nice life". You may even be perp-walked out of the office in front of your coworkers. To the modern employer (with very few, but very notable exceptions), you are a cog. Just about any employer saying otherwise is lying to your face to try and eke out a few more units of productivity before you burn out/leave/get fired. Conduct yourself accordingly.