No hard implications, but it might influence how you number the days (C99's tm_wday uses 0-6 with 0 = Sunday, which suggests a week starting with Sunday, partic

No hard implications, but it might influence how you number the days (C99's tm_wday uses 0-6 with 0 = Sunday, which suggests a week starting with Sunday, particularly since tm_mon uses 0-11 with 0 = January, but is also compatible with the way the days are numbered in Chinese, with Monday = 1), and it might be related to how you work out which months have 4 weeks and which months have 5 weeks: it's unusual, but some part-time employees get 4 weeks' pay at the end of most months but 5 weeks' pay at the end of some months, bizarrely.