A lot of mescaline/cacti trip reports note a slowing or stopping of time.

Do you experience this as everything around you appearing to slow down or stop, and you can observe this happening in normal real-time. Or is it more subtle, such as looking at the clock/watch and thinking 'Flip, is that all the time it is? I thought it'd be 5pm by now, and it's only 2pm'?

Yes, the effect is literal. One manifestation could be looking at car go veeeery slowly when it's directly in front of you, and at normal speed when you see it with the side of your eye. Music could also appear to sound slower/faster than "normal".

The second sensation you describe is more attributable, in my opinion, to being or not being thinking of the passage of time and instead being immersed in the trip.

That sounds terrifying... lol Yes I'm a woose, but I think that would be quite unsettling. Does the mescaline set one in the right frame of mind for accepting such an observation?

Mescaline has given me time dialation to the point of time slipping/fragmentation, that soon manifested as basically time travel.

I experienced time breaking down into frames, with each frame stacking, or overlapping previous and future frames. Each frame from either the future or the past began to take on a life of its own as well, and communicating with the present frame or "me", seemingly reaching out across time. It was very frightening and I thought I was ging to be commited to be honest. I took off into the bush leaving all my friends behind and spent many hours alone, walking non-stop. I walked a far distance through the city following the ocean, time traveling and periodically stopping a different beaches to try to get ahold of myslef.

Cannabis had a played a large role though. Cannabis in high doses facilitates time distortion and time travel for me. I had smoked cannabis about 6 hours after I started consuming the cacti, and I hadn't had it in many weeks prior so there was no tolerance.

The same thing happened to me about 2 months ago after drinking 80g of caapi. I thought the caapi was basically finished with me after about 3 hours so I walked to the beach wth minxx and we smoked. I took one large hit and that was it. It was so much like that time with cacti, just a little less intense.

I dont get near cannabis with other entheogens anymore.

Wow! It's all so incomprehensible to me at the moment. What dose of mescaline did you take?

It was actually very interesting and enjoyable (the time dilation was somehow manageable). I knew that it was just the effect of a drug and that it'd pass, although it was a very strange feeling at the beginning, to be frank.

watch the matrix

then watch inception
(inception is all about time dilation)

Yeah I've seen both, but I wondered how mescaline affects how the user perceives time qualitatively.

In Inception everything appears in real-time to one's self however, so how would that compare with mescaline time dilation?

I think it's similar to how one perceives time while in a dream. As is mentioned in "Inception" the deeper into a dream you go the slower time seems to move. A similar effect can be experienced with mescaline. I've noticed it especially when listening to music or watching a video of some kind. With eyes closed the effect is increased exponentially.
On one trip I can recall a vision in which I was in a desert of some kind watching what looked like a piece of tattered clothing hanging off a broken fence. It was waving in the wind at an incredibly slow speed. I was able to observe every motion in a frame by frame sequence. It then began to unravel; first thread by thread and then each molecule began to rip apart. Just like in a dream it seemed to last for hours but I know was only a few minutes.
It's really quite strange how it is able to alter our perception of something as fundamental as time in such a profound way.