My suggestions:
I use NoScript, so I have to initally allow the right scripts to use a site like this. However, before I did this, the initial error message it tried to show to remind me to enable JavaScript was cut off at the bottom, and I couldn't read it.
Color scheme and formatting are garish and the sidebar and text spacing look haphazard and poorly aligned. It can give one the impression that the site is amateurish.
Excessive use of JavaScript. None of the links can be opened in a new tab/window. I'm forced to left-click ads, which leaves the site, and this resets the 300-second timer when I return!
The danger with implementing the timer in user-side JavaScript code is that someone can trivially manipulate how their browser executes the code and circumvent the timer, unless you actually have some server-side code keeping track of all the requests or something so it can determine how legitimate the browser response looks.
Edit: I would also suggest mentioning how often one can request free bitcoins right on the main page somewhere. I had some trouble finding this information (especially since I initially had some trouble getting the “how it works” link working due to the JavaScript/middle-click issue).
