"Vinyl has gotten to the point where it's exclusive for the collector." — Josh Homme (Queens of the Stone Age, Eagles of Death Metal)
It is possible to cut records up to 30 min per side, and our times per side calculator is not intended to say what can and can't be cut, but rather to indicate the sound quality potential available on a one-cut (unattended) attempt on customer supplied audio files. Yes, there are some famous albums from Pink Floyd and the likes with long times per side and you can be sure that they didn't arrive at the final sound with a single cutting attempt on a given set of masters. Numerous (by this I mean a dozen minimum) mastering + cut + test pressings, then remaster + recut + repress TP's batches were done before the production team would sit and listen to these cuts to evaluate which was better etc. And this is all possible with money, lots of it.
So yes, 30 min per side is possible on vinyl but not on a one-attempt (unattended) cutting process and perfection is possible at a fairly high price. Bear in mind that the production and mastering people involved with those bands/labels knew very well the sound quality drop-off due to long running times, and would spend lots of time managing and setting up track positioning, mastering etc (lots of mastering tricks that are long forgotten today with digital) to suit the reduction in overall volume to minimize the impact. There is also the unknown variable of whether some were cut on DMM or lacquer.
The constraint with long times per side is that all of the real estate available must be used for the cut, which means from the outer edge all the way to the center. You can compare a thousand releases with each other and you wouldn't be able to establish a pattern between them on why one sounds a certain way with a given lengths vs another with a different audio length. Vinyl is analog and bound by physical limits that are real and not to be ignored. The simple rule is, the longer the time per side, the more loss of sound quality potential there will be. The time per side calculator is accurate in it's indications and I would recommend that you rely on it for what to expect based on the times per side you have.
The more time recorded on the record, the more revolutions the record turns, making for a longer groove, and hence a thinner - shallower groove.
With computerized pitch, the grooves are placed right next to each other when there is little or no volume. Since the louder recordings require more vibrations, the needle deflects sideways, and possibly into the adjacent groove causing a skip. To prevent the grooves from colliding, the computer adjusts the spacing between the grooves to make sure they do not collide and cause the record to skip.
Therefore, if the recording is long, the grooves are shallower. If the recording levels are louder, there must be more space between them. Another effect of long times per side technically explained. For example when a vinyl record is spinning at a standard 33 rpm (or 45 rpm). The stylus begins at the outside edge of a standard record and moves slowly towards the center over the duration of play time. Laws of motion dictate that, under a constant angular velocity, a point at the outer edge of said record must inherently move at a faster speed than a point near the center.
While the record spins at the same rate at the outermost and innermost portion, the amount of vinyl the needle encounters is reduced as it works its way to the center.
Say you took a piece of string and wrapped it around the outer edge of the record. For a 12” (diameter) record, the string would be about 36” long. If you wrapped string around the innermost groove, you’d have a 4” diameter circle and about a 12” length of string. The needle traverses both these lengths of strings in the same amount of time. So if it takes the needle one second to trace the entire circumference of the record, it would be traveling 36” per second at the outside and only 12” per second towards the middle. This is effectively like recording on analog tape at 30 ips at one end of your album and 15 ips at the other end.
So cutting further out towards the outer edge (when time per side permits this) is the technically correct way to maximize sound quality potential and minimize sound alterations/deviations, which can amount to better playback (on properly mastered audio). Using up the whole surface on long time per side cuts (or for the fun of it) will have a negative effect on sound quality.
Stereo cutting works by making a v shaped groove. In a very simplified explanation that means one channel (i.e. left) goes in the depth (up and down) while other channel is cut laterally (left-right).
Obviously the limitation is in the depth, and you are talking about fractions of a mm. In other words, the space for a groove is physically limited to fractions of a mm. Ten minutes of average audio at the maximum possible level will barely fill 1/3 of a 12" side. When a short cut fills a side it's not because the engineer has done a "fat" cut, it's because they adjusted the lathe to put more space between grooves simply to avoid discussions like this.
People who don't understand cutting think they are getting more "value for money" by filling the side but it's completely false unless it's actually a long cut (which is also ill advised).
Sound quality at the center of a 12" is up to FOUR TIMES worse than the outside. Any cutting engineer who is experienced therefore would try to avoid cutting to the center wherever possible.