The purpose of the mash is to allow you, the brewer, to present the sugar profile you desire in the fermenter to make the beer you designed.
At 45 min starch conversion is (almost, don't worry about it) always converted to sugar, "Conversion" complete.
After conversion the enzymes are still hard at work breaking long chain (non-fermentable) sugars into short chain (fermentable) sugars.
All this action is controlled mostly by temp and time. The 154F mash temp indicates that you wish to make a beer that has a residual sweetness. The "extra" 25 minutes will tend to lessen this somewhat, and there is nothing wrong with that!!! I have mashed beers for 4 hrs, some brewers mash overnight.
There is really no hurting the mash, there is really no "wrong" way there are different actions that change the character of the resulting beer.
The bottom line is how does the beer taste?
Fred