of + ter, æfter [OE]
after [MI]
https://www.etymonline.com/word/after#etymonline_v_5222
https://www.etymonline.com/word/off#etymonline_v_2510
https://www.oed.com/dictionary/after_adv
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED802
https://bosworthtoller.com/9071
https://bosworthtoller.com/450