Always remember, that what you have in back end doesn’t need to be the exact same thing as in front end. Separate data (model) from view. For example save a high score as just a plain number in e.g. ms and then, only when you want to display this number in any format you would like to have, convert it just before displaying 
For operations (comparisons in this case probably) use just a plain number, but what you display to user might be then presented in any way you want it
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