The length of the betrothal period is not specified in the Bible. We might reasonably suppose that it was not indefinite, but a period agreed upon at the betrothal.
See information from the Jewish Encyclopedia: http://www.jewishencyclopedia.com/articles/3229-betrothal
The betrothal period is given as 12 months.
“After the betrothal, a period of twelve months was allowed to pass before the marriage was completed by the formal home-taking ("nissu'in," "liḳḳuḥin"). In case the bride was a widow or the groom a widower, this interval was reduced to thirty days”
In terms of the church, betrothed to Jesus Christ, the betrothal period for individual members obviously varies and is unspecified. But the date of the marriage has been fixed by God and will not change.
I hope you find this helpful.