The reset in a castsequence macro starts with the first press of the macro sequence.
Not the most recent press.

It's very easy to test this...

/castsequence reset=5 Spell 1, Spell 2, Spell 2, Spell 2, Spell 2, Spell 2, Spell 2, Spell 2, Spell 2, Spell 2, Etc..
Spell 1 will regularly come up every 5 seconds.
sorry, this is wrong, the 5 seconds are count from the last activation of the macro, as also statet in the Thread you mentioned:
reset=n/target/combat/shift/alt/ctrl

Where n is a number of seconds. You can specify any number of these conditions separated by slashes as shown. Seconds are used as a timeout for the command. Each time the sequence runs, it resets the timer. If you don't use the macro within the number of seconds specified, the sequence will start over. This is a very important distinction because it means you cannot use a reset timer to account for cooldown. target resets the sequence when you change targets; combat when you leave combat; shift, alt, and ctrl when you activate the macro with one of those keys depressed.