Agreed, 3:25 means Twenty-five minutes past Three O'Clock but I've never seen that notation to mean three hours and twenty-five minutes. The notation 3.25 means three and a quarter hours. The only way I know to express Three hours and twenty-five minutes in just numbers and punctuation is 3 5/12 hrs. There is no decimally exact way to express it.
Note there is a similar method used in baseball when recording the number of outs a pitcher records. Since an inning has three outs and you want to say that he (sorry ladies) pitched 2 and two-thirds (2.666...) the current convention is to state it as 2.2 innings, Two point three innings would be the same as three point zero innings, So, the types of notion you'd see in a statistics list for baseball pitchers would all end in point zero, one or two. It makes sense in the context if you know the convention. In the time problem, the convention of twenty-five minutes being expressed as point two five flies in the face of the convention widely accepted that point two five equals a quarter hour and nothing else.
"...Tomorrow's come a long way to help you."
Tim Davis 'Your Saving Grace' Steve Miller Band (1969)
"...Yesterday's at least a mile back."
Dale Peters 'Dreaming in the Country' James Gang (1971)