1. 'All I have to do is just do it!' or 'All I have to do is to just do it!' -- they are both grammatically fine. The second 'to' is unnecessary, especially in this offhand remark.
2. 'Time passes by too fast' or 'Time passes too fast' or 'Time passes too quickly' -- all again are fine. 'Fast' is slightly less formal that 'quickly'. 'Passes by' suggests to me a lackadaisicalit
"Alack(=Alas) a day!"="Woe worth the day!" ... an interjection expressing sorrow. (EX) She is dead, she is dead: alack a day! [Shakespeare : Romeo & Juliette, 1592] It's sometimes exclaimed as "Lack-a-day", and adjectivized into "lack-a-daisical" (=sentimental, vigor-less, languish, lazy, indolent).