I'm trying to better understand the Offertory Chant in its relation to the Mass (TLM).

The Introit and Communion are related to procession, and their duration and style match accordingly.
The Gradual/Alleluia take as long as they take; meditative psalms that hold their place among the readings.

The Offertory...I have heard as the musical offering, made in conjunction with the offering of the bread and wine, but maybe that's not the whole picture. Is it practically meant to last until the incesation of the altar begins? The offertory varies in length much more diversely than the Introit and Communion, so it seems to be a "as long as it takes" approach, not entirely unlike the Gradual/Alleluia. There are also the ornate Offertory verses that can be added to extend the chant, but what is the practical coverage that the offertory is meant to serve?

I understand that many will use the time after the Offertory chant to offer other hymns or songs that they find suitable, but I first want to better understand the nature of the Offertory. For example, I recently learned that the communion is short for a Sung Mass because practically no one, historically, received communion except the celebrant, meaning that anything longer would have expanded the chant past its role in the overall liturgy.