The Gillock piece only took a single session yesterday, compared to the Mozart at 3 days.
The longest quick studies for me are rock pieces with their tied notes for syncopation. My slight dyslexic tendency confuses them with slurs. I haven't done any rock pieces yet this year, but I remember at least one last year that took me 3 weeks.
1 Michael Head, The Quiet Wood, The Best of Grade 1 Piano (quick study)
2 Joanne Bender, Ripple Effect, RCM 3 Piano Etudes (regular piece at my level)
3 Henry Mancini (arr.), The Pink Panther, Piano Adventures Popular Repertoire - level 3A (quick study)
4 American folk song, Shenandoah, Piano Adventures Level 5 Lesson book, (regular piece at my level)
5 Mozart, Allegro in F, K. 1c, The Best of Grade 1 Piano, (quick study)
6 Gillock, Owl at Midnight, Accent on Solos (early to later elementary), (quick study)