Selected Answer
Excel has a function DATDIF (undocumented under Fx) which can do this. Just put this in a cell:
=10*DATEDIF(DATEVALUE("15/01/2021"),TODAY(),"M")
and change the date in bold to your locale/ 2020 if accrual in cumulative over years.The DATEDIF function returns the number of months since the first date(with hte argument "M") which is then multiplied bu 10 (hrs/month) to give the total accrued hours.
You will need to format that cell to General or it will appear as a date.
Alternatively try putting your start date in cell A1 and use this instead:
=10*DATEDIF(A1,TODAY(),"M")
Hope this helps.