Don't do it. There are a lot of factors that you are not aware of, particularly on shallow dives, that could do serious harm or kill you. You need to understand how depth affects air in the tank and in your lungs. At the depths and times you are talking about you almost certainly won't get bent but there are far worse things that could happen because of inexperience and lack of understanding of a number of factors.
In addition, venturing into an overhead environment with no penetration training is seriously stupid. Going into an overhead environment without even open water scuba training is simply begging to recieve a Darwin Award. In case you don't know what that is - it's an award given to people who die doing something so outrageously stupid that they should not live to breed - survival of the fittest in it's purest form.
Stick with snorkeling till you save up enough to get certified. Then rent equipment till you save up enough to buy your own. A mask, fins, and snorkel are affordable by nearly everyone.
Even though I have a number of advanced certifications I often snorkel because of the freedom from equipment that snorkeling offers, the lack of any time restraint (I can stay in the water for as long as I want - usually hours). I often snorkel places that I would never bother to gear up to dive - very clear, shallow rivers, for example. It's amazing what you can see from the surface. Be satisfied with that for now.