There are quite a few methods actually for finding times related to marriage and relationships. Of course, we have Venus as the natural significator of romantic relationships in general. But we also have the Moon which naturally signifies marriage, according to Valens. Then we have the accidental, or as I prefer to call it, "circumstantial" significators of marriage, which are the the lord of the 7th place and the sign of the Lot of Marriage and its lord. Some authors may also consider the 10th and/or 4th places for marriage (iirc, Ptolemy and Valens).
Just as there are several approaches to interpreting the father (Sun/Saturn/Jupiter) and mother (Moon/Venus), similarly marriage is also considered by Valens using several different approaches. Valens presented at least two versions of the Lot of Marriage, Jupiter/Venus, and secondly either Sun/Venus or Moon/Mars for men and women respectively. Maternus also had several Lots dealing with marriage, although they do not have the same names.
In terms of time lord methods, in the sole example on Decennials given by Valens, when the period was handed over to Venus (Level 3 lord), matters concerning the wife came up. Decennials is similar to Firdaria in that planetary periods are used to derive the time periods, and that the planets, not the signs, have rulership over the times.
In zodiacal releasing, according to what I've read in an article by Curtis Manwaring, either Fortune or Spirit may give indications of marriage when the rulership is handed over to the signs and/or planet related to marriage. In Schwarzenegger's example, it was the Lot of Spirit, and the 8th place, which was ruled by the ruler of the 7th place, was activated, resulting in marriage.
According to a chapter in Valens where he talked about the second method of finding the Lot of Marriage, he said that the Lot should "agree with" Spirit for men, but with Fortune for women. This led me to infer that we should probably release from Spirit to find marriage for men, while for women we should release from Fortune (although there are complications and/or exceptions, when the Lot is cadent from the Ascendant).
However, this is just a hypothesis, so it is not established yet. I need to research some real charts to determine its veracity. When I have the time...I really should be doing something else right now X_X.
With all this in mind, the conclusion that I would draw is that when using whatever time lord methods, including the firdaria, we should look at all the significators that are related to marriage, and not just the 7th place. Also remember to evaluate in the natal chart whether marriage is likely in the first place!
Hope this helped,
Larxene Xenohart
EDIT: Edited wrong information about zodiacal releasing.