Depends
It depends on how you do it. If you are careful on how you raise the bets you can get away with it for a good while. Most books and articles have sections on cover betting. If you only increase after a win and do not decrease until a loss it can buy extra time. Letting a big bet ride to the next shoe once in a while and taking insurance on small bets occasionally. Make them think you are a gambling sucker. 2 hours may be a bit too long though. 2 hours on a big loss might be ok....but not if you are winning big. Never walk away with a monstrous win. Also...never never stay to get even unless you are not returning to that casino for a very long time. Those two actions will attract a ton of attention and they will disect your play by default. These days with the software they have for analysis you really are stuck once they flag to analyze you.
The above can be ignored until green or black chip play.
It seem you are taking the same approach I took. I had a fairly local town not too far away and that was my traning ground. Trying to be a decent AP was a hobby. I would sit at the tables for hours on end. Occasionally I would see other AP's and two of them could not believe how long I would sit at the tables. I have now elevated my play from hobby to part time job but I am ruined in that town. I cannot play BJ at one casino and I get really ugly looks at the others. I cannot employ cover play because they know me by name and face and also know I am a very smart player. I often corrected the dealers and the pit bosses. Big mistake but I was a know-it-all and couldn't help myself. The really sad part is that I am down in that town by several thousand. I can't say I wish I had played it differently because it took going through that to learn the lessons.
Krill the G