The general rule of thumb in chemistry is that every 10 degrees celcius (18 degrees F) doubles the reaction rate. There will be limits to this of course and different reactions can occur if the temperature is raised too far. Think of it as the difference between baking a cake and burning cake batter.

Check page 4-17 for a table on temperature versus treatment efficiency. 4-19 also has an interesting table.
http://www.epa.gov/ogwdw/mdbp/pdf/alter/chapt_4.pdf

The short version is, 30 minutes is likely more than enough time using the manufacturer recommended dosage for water temperatures one is likely to actually drink.