What type of vow is this, and what are the resulting sins and expiations, and must it be fulfilled within a specific period or not?

This vow is an absolute vow, and it is recommended and must be fulfilled in the manner in which the vower vowed it, based on the hadith: "Whoever vows to obey Allah, let him obey Him." The vow should have been fulfilled at its specified time, and if you were preoccupied, then be sure to hasten to fulfill it as soon as possible.