Re-reading the OP, I see he/she lists a 1:28 instrumental. Well, I’ll see you and raise you two:
Wonderwall To Be Here by George Harrison at 1:27
and
Sparrowfall 1 and 3 by Brian Eno at 1:10 and 1:23 respectively. (2 is 1:40).
They are all truly great pieces of music.
I’ll throw in two that might not qualify as all-time greatest but worth a listen, particularly if you’ve never heard them before.
Jethro Tull’s version of Bach’s Bourée. Link
Evidently the boys wanted to do a souped up version of a classical piece and somebody in the group, probably Anderson, suggested this one. Reason? He had lived in a flat where a classical musican neighbor practiced this piece endlessly.
Eddie Van Halen’s **Spanish Fly **demonstrates why his mug should be part of the Rock Guitarist’s Mount Rushmore. Link
Chuck Leavell’s horrible piano solo. Really ruins the song.
Listen to “In Memory of Elizabeth Reed” instead.
Other favorites:
“Catherine Howard” by Rick Wakeman
“Repent Walpurgus” by Procol Harum
“Soul Sacrifice” by Santana
“Slightly All the Time” by Soft Machine
“Underture” by the Who
“Glad” by Traffic
“Peaches en Regalia” by Frank Zappa
“Bombay Calling” by It’s a Beautiful Day
“Atom Heart Mother” by Pink Floyd
In addition to many mentioned already, I’d have to go with Prince’s “Alexa de Paris” and the B-52’s “Follow Your Bliss”.
And possibly Metallica’s “To Live Is to Die”. But “Orion” is far superior.
Shit! How could I have forgot “Satch Boogie”, by Joe Satriani?
I have always enjoyed the instrumental parts of ‘Magnum Opus’ by Kansas.
The live version is on my permanent playlist.
Please note that the you tube version in the link is not the one I have, and the recording quality is a bit below my standards.
Also, if you can count this as an instrumental: “One Step Beyond”, by Madness.
And Metallica’s “The Call of Ktulu”.
For my money you could cut this off at the 2:06 point and have a nice instrumental. Virginia Tech thinks so, anyway.
Speaking of surf music, Wipeout by The Ventures deserves a mention.
But the Allman Brothers’ Jessica is the instrumental champion in my book.
A lot of my favorites have already been mentioned, but here are a few more. Includes a bunch that are almost rock, or by rock artists on rock albums but are more jazz or other genres, or whatever but they’re still good:
“Gold and Silver,” “Edward, the Mad Shirt Grinder,” “Spindrifter,” “Cobra,” Quicksilver Messenger Service (what a great band for instrumentals)
“Sunny Side of Heaven,’ Fleetwood Mac
“La Fuente del Ritmo,” Santana (and most of thre rest of the Caravanserai album)
Abaddon’s Bolero," Emerson, Lake & Palmer”
“Flute Thing,” Blues Project (like with “Elizabeth Reed” I go back and forth on whether the original or the live version is better)
“Zémio,” “Breakdown,” Joe Jackson (from the almost unknown Mike’s Murder soundtrack album)
“Percolatons, Pts. 1 & 2,” Gong
“Mistress of Storms,” Bruce Cockburn with Gary Burton
“Icarus,” Paul Winter Consort
…and check out this crazy video for Preston Epps - “Bongo Rock” (1959)
ELO’s “Fire on High” deserves a mention here. There are some brief, intentionally-reversed lyrics around 0:30 - 0:45.
The Alan Parsons Project has some nice ones --“Lucifer” and “I Robot” to name two.
I also heartily second Tomoyasu Hotei’s “Battle Without Honor or Humanity”.
Savatage’s “Christman Eve/Sarajevo 12/24” (based on “Good King Wenceslas” and “Carol of the Bells”) is also worthy of this thread. Some of the members of Savatage later went on to form the Trans-Siberian Orchestra, which famously performs this song and other Christmas classics all over the world.
Those are among the ones I wanted to mention. 
Also:
Sleepwalk, by Santo and Johnny
Cinema, by Yes. I always thought this one would be perfect for doing team introductions at the start of a ballgame.
Yeah, it’s their song - but Brian Setzer’s version isthe scary-good amazing one. Be prepared to put down your guitar.
“Wipeout” was done by the Surfaris. The Ventures covered it, but the Ventures covered everything.
“Walk, Don’t Run” was a Ventures original, I believe.
I haven’t seen “Albatross” by the original Peter Green incarnation of Fleetwood Mac mentioned. You’ll never hear tastier guitar.
And if you want to go all the way back to 1960, I love “Apache” by the Shadows!
Ignorance fought. Thanks.
Yes, it’s cheesy but crossroad guitar duel
Oh, oh!! I have some!!
Some more from the Allman “family”;
Pegasus
Kind Of Bird
Sea Level - Tidal Wave
Sea Level - Storm Warning
Gov’t Mule - Afro Blue
Derek Trucks Band - Kickin’ Back
Carlos Santana - Cry of the Wilderness
Santana - Europa
Grand Funk - Flight of the Phoenix
Little Feat - Day at the Dog Races
Little Feat - Stomp (soundcheck)
Dixie Dregs - Take It Off The Top
Jeff Beck - Freeway Jam
Jeff Beck - Blue Wind and another version with Jennifer Batten
Joe Satriani - Always With Me, Always With You
Joe Satriani - Echoes