Unfortunately, you can't make a probabilistic estimate if you will contract heart disease or some form of cancer - there are too many variables to consider. How big is the room? How many people are smoking? Some people smoke all their life and die without cancer or disease - though poor lung function. But I found some interesting information, we can use it to make an estimation:
It is estimated that only 15% of cigarette smoke gets inhaled by the
smoker. The remaining 85% lingers in the air for everyone to breathe.
If a person spends more than two hours in a room where someone is
smoking, the nonsmoker inhales the equivalent of four cigarettes.
Secondhand smoke is the third leading preventable cause of disability
and early death (after active smoking and alcohol) in the United
States. For every eight smokers who die from smoking, one innocent
bystander dies from secondhand smoke.
Enclosed smoking areas are far more toxic than exposure to second-hand smoke from bystanders outside. Anti-smoking campaigns (rightfully) tend to exaggerate a bit, if there's one person smoking one cigarette, you won't absorb four cigarettes... So my estimate is that within your 4 hours you will absorb 1-5 cigarettes worth of toxins, depending on how many people are smoking, how large the room is, and how well ventilated it is.
A one-time exposure for four hours is definitely statistically negligible, but it sounds like you want to do this regularly. 4 weeks in a month are equivalent to 4-20 cigarettes smoked. In a year that's exposure equivalent to 48-240 cigarettes. Let's say you will not go to the casino three months of the year, and we take the average of that estimate. That puts you in the ballpark of 120 cigarettes a year, or 1/3rd of a cigarette per day. Clinically, smoking is estimated in pack years https://en.wikipedia.org/wiki/Pack-year and this estimate is far below a pack year - there are no studies concerning such a low amount of consumption I could find.
But it still boils down to regular exposure to carcinogens, which one way or another raises your risk. Smokers go through much more tobacco, so studies are hard to find for such a low exposure, but it is definitely significant. If you go to the casino once a month for 4-5 hours you will be fine. But if you're concerned about long-term health I wouldn't go every week. Also gambling can be more addicting than tobacco. ;)
Hope this estimate helps you.