@Tim's rule of thumb about duration is definitely solid. The rate of chord changes - called harmonic rhythm - is generally around two chords per bar for a fast harmonic rhythm to about one chord for two bars for a slow harmonic rhythm.
But, I would apply two other guides:
- keep to the simplest harmonic description that shows the clear tonal functions
- and Schoenberg's adage: follow the bass.
Dm - Dsus2 - Fmaj - Cmaj
I assume these fingerings...
Apply the other two guides...
Simple harmonic functions: is there a functional difference between
Dsus2? No. The root doesn't change which is a pretty good indication that harmonically nothing is happening. Additionally, in the major/minor system of harmony where fundamental chords are major, minor and diminished triads, is
Dsus2 really a bona-fide chord? No.
Apply Schoenberg's adage. Literally, follow the bass, ignore the details in the upper voice(s). Again the bass isn't changing, the root isn't changing. There isn't a harmonic event.
Do not misunderstand this to mean the
Dsus2 is not important.
The point is
Dsus2 represents melodic events rather than harmonic events.
Duration doesn't matter too much. You could play
Dsus2 as a quick pull off and go straight to
F. Or, you could play all four "chords" with a quarter note stroke and give a full bar to each. Either way the
sus2 part is just a non-chord tone decorating the proper chords
Dm - Dm - F - C.
In everyday speaking
Dsus2 will be called a "chord." That's just plain ol' natural speaking. But in the context of this question of passing note versus chord - it's not a chord, it's a neighbor tone.