As close as I can reckon it, there was about 20 years between God's promise to Abraham of a son and heir, and the birth of that son: Isaac.
Muṋe washu a sinyuwa musi wonoyo a ana a ri, 11'Zwino nge vha si ntevhele nga mbilu yoṱhe, vhanna vhoṱhe u bva kha vha miṅwaha ya 20 vhe vha pfuluwa Egipita, a hu na na muthihi wavho ane a ḓo vhona shango ḽe nda ḽi fulufhedzisa Abrahamu na Isaka na Jakopo nga muano.' 12Vhe vha khathutshelwa mbilu ndi vhavhili fhedzi, ndi Khalebe ṅwana wa Jefune wa Mukenisi na Joshua ṅwana wa Nunu; havho a vho ngo vhuya vha shandukela Muṋe washu.