Mr. Barakat,

Since your project isn't a homework assignment, is it vocational or avocational in nature? In either case I would suggest that you take the time to search this forum for material regarding the accuracy of µ-controllers/crystals as timing standards, especially if this is new to you. Search on "timing accuracy." You may be surprised. Then, if you have the time, do the math just to round out your understanding.

And yes, if I were working on a similar project I would incorporate an RTC as well. But frankly there are others on this forum far more versed than I to offer specific RTC advice.

Again, Good Luck.

P.S. It is "..., do the math,...," not "..., do the maths,...." If you just want to use a plural form, then it would be "calculations," not "calculation," unless of course all of the math were expressed succinctly in a single calculation.