So past tense would be 'Uaireanta, rith sé abhaile'? Is this sentence in this section (present tense question in lesson on past tense) to catch us out, by accident or to demonstrate a particular point?
It sounds odd for me to use rith there. I'd say ritheadh sé would be better, since it's habitual. (Sometimes, he used to run home, which sounds odd to me in English). Still, however, I'm not sure how good that is in Irish.
instead of uaireanta, i would usually use Scaití which means sometimes as well.