yes, Jesus bids us to 'pick up our cross and follow Him' - this means doing as HE did, which is being righteous, in thought and deed, and for most of us this takes a great amount of practice and change!

but the only set fast i know of in the bible is the day of atonement - other than that you do it as you decide, no one is to decide for you just as no one should decide what you eat, which day you sabbath (if at all, your choice) as long as you love God with all your heart and love your neighbour as yourself.

where are you from friend?