since; a certain length; as long as; as far as
eko- is the form of the relative preverb ako- in changed conjunct verbs without any preceding preverb.
Mii 'i zhigwa aabito-diba'igan gaa-ako-bimwewebizod.
It's been half an hour now since we heard him go by.
Gii-migoshkaadendam gaa-ako-wani'aad iniw ojiwaaman.
He's been really bothered since he lost his friend.