In this case you can delete the U in (?siU). The U means "ungreedy" and catches only the minimum of characters of a class.
So at the beginning a "(?siU)Minutes : ([0-9]+).*,..." captures only the first digit of "Minutes : 1000,..."
the [^,]+ at the beginning means: capture everything but a ,
the [0-9]+$ at the end means: capture all digits at the end of the string ($ means "the end of the string")
Beside ikarus1969's reply, I'd note another thing too. Although I'm not using the Python plugin and I don't know how it does work, I suppose that your code doesn't work because then [MeasureChild1] WebParser measure should have to be updated when the [measureInfo] measure gets its value. There are two possibilities:
If the Python plugin measure does support a FinishAction option, it's much easier. Just have to add a FinishAction=[!CommandMeasure "MeasureChild1" "Update"] option to the [measureInfo] measure. However I think this solution doesn't work, because it seems the Python plugin measures don't support the FinishAction option.
If it indeed doesn't support the FinishAction option, there is needed another approach. Try to add to the same [measureInfo] measure, the following option: OnChangeAction=[!CommandMeasure "MeasureChild1" "Update"].
Again, since I'm not using the plugin, I'm not sure if any of these solutions will work, but maybe it worth a try.