The GoBD are Germany's principles for proper keeping and retention of books, records and documents in electronic form. They also apply to digitally recorded working time where it is tax-relevant.
Spreadsheets and paper slips can be changed unnoticed and usually fail immutability. During a tax or FKS audit this can lead to objections.
Yes, where the records are tax-relevant (e.g. as a basis for wages). The principles of immutability and traceability apply accordingly.
Usually not, because it can be changed unnoticed afterwards. An audit-proof software solution is preferable.
Depending on purpose, 2 years (MiLoG) up to several years for tax. EmployGuard retains proof on time.