あっという間に１０日経ったって英語でなんて言うの？

あっという間に１０日経った - 10 days went by just like that 経つ - go by, pass (by) あっという間 - in a flash, in no time 10日間の研修があっという間に終わった - 10 days of training flew by / 10 days of training went by so quickly / 10 days of training went by just like that