Elven Spell Song Questions

How long does the elf have to continue singing AFTER he has fulfilled the action cost to check his success?

For example, A sword singer uses “singing blade” while drawing his sword to gain the open-ended sword dice effect, an Ob 2 effect that takes two actions to produce.
Does he have to continue singing to continue the effect, or can he stop singing once the effect has taken hold?
(the first way seems correct to me, but I’ve seen some old “character burner” threads that make me question this)
The second way would treat it more like a “sustained spell” with constant singing doing the sustaining.

Wouldn’t “Let it Ride” dictate that the spell song roll would stand for the duration of the scene?

Song of Merriment seems as if it takes longer to sing than its effects would dictate the need for the song (hesitation shouldn’t last 120 actions for anyone). That’s (basically) 30 exchanges in Fight! 6 in DoW, and 6 volleys in RaC.

Laments are also on the long side, some of them would not be possible for an elf to sing by himself to completion in order to ease his own grief (Lament of the Westering Sun takes an entire day from sun-up to sundown, or approximately 12 hours), even passing songs off with song of songs or duplicate spell song doesn’t help ease your personal grief unless some leeway is taken with what is meant by “individually”
Suppose several Wilder Song Singers gather to lament the passing of their mentor, as they pass the “Westering Sun” amongst themselves, each deals with their own grief during their stanza.

But that’s not RAW.