Without a specific inducement, warrants are not generally exercised until close to their expiry date. 

One exception is if the warrant holder needs the money, they would either sell the warrant (do our .52 warrants trade publically?), or exercise and sell the stock.

Another scenario has to do with an enticement from the company, which might include a "favor" in connection with a future financing, or a clear and convincing argument about how the warrant money will be used and why that's good for both company and shareholders (in this case, specifically including shareholders as a result of early warrant exercise).   

These warrants were probably valued around .16 or so when they were issued as part of the .36 unit (that was my ball guess at the time, and some evidence of that value was provided by the market valuing our stock in the low .20's not all that long thereafter. 

Does it make financial sense to exercise and spend .52 now for a share if you intend to hold onto the stock long term, when you can simply hold the warrant and later determine if it makes sense to exericse?  One week from expiry, what if the stock is at .25 - you would be a significant loser had you exercised and paid .52.  If the stock is at $2.00, you exercise then.

So, for any that were unclear, the above is why a warrant holder (who believes in the company long-term) does not typically exercise until near expiry.  Nevertheless, there are times that they will, often tied to some inducement or other.