Google Sheets – Add Up Time Used in Minutes for Spreadsheet or Doc Table

Formatting is not the answer, because it doesn't affect the underlying values. You need to make the values updatable instead.

One way is to make a reference-data place somewhere in one of your sheets (or maybe add a new sheet just for that), and put the year value in there.

Then in the first cell where you want the date values to appear, use this formula:

=date(B1,01,01) except replace B1 with the value of the cell where you put the year value.

In the cell immediately above or beside it, say =D1+1 except replace D1 with the reference to the cell where you put the first forumula.

Then to make a new file for next year, just save-as and change the one reference value.

Apologies for the long and convoluted formula, but this assumes the values to be summed are in A1:A5 (some of those cells may be blank and will be ignored, but in it's current form the range has to be vertical and no more than one column wide), that these values are text strings in the format that you described, and that you are set to a locale that does not use a comma for a decimal point:

=ArrayFormula(JOIN(":";TEXT(ROUNDDOWN((MOD(SUM(REGEXREPLACE(A1:A5;"([0-9]+):([0-9]+)";{"$1","$2"})*{60,1})/60;{1E293;1})+{0;0.01})*{1;60});{"0";"00"})))

edit: based on Jacob Jan Tuinstra's comment that pointed out an inaccuracy, I have had to make it even more convoluted to mitigate against an occasional floating point error; this is the reason for the +{0;0.01}.