I had a really strange event where I had at least four cessations within a roughly 30-45 minute period. Is this normal for some people? The cessations were rather short in duration. 

I wrote this about an experience I had:

I experienced this phenomena where it was as if I was having flashes of experiencing myself outside of my body as another me for a split second before reconverging into one me. It was like my sense of self was being split in two. It seemed like I had visual flashes of my body that gave this strong sense.  I was experiencing those flashes every few seconds or so, and I had a period of about 5-10 minutes where the flashes of two me/one me were happening so rapidly that that seemed to take up my whole field of experience and I was investigating what it felt like and just being swept into it. Cessations would happen rapidly, one after another, and at the crescendo of this thing I had this this sense of being obliterated or annihalated by the cessations and it seemed like there was more cessation than non-cessation they were so rapid and it was distinctly creepy and scary but was also pretty blissful.

I chalk this up to tuning the mind to conformity knowledge and wiggling between the no-self door and frution. So I guess your answer is "instantaneously/as long as conformity knowledge lasts" YMMV.

I've had a similar experience to what you described. Thanks for sharing 

Yes, there was a phase when I lost count because they were so many. 

This is in fact one of the common "determination" (aditthana) exercises in the Thai-Mahasi lineage, after reaching equanimity. For some reason they call it "phenomenon of arising and ceasing" (which has nothing to do with A&P), momentary unconsciousness or (as I understand it) "short" fruition or almost-fruition (if that makes sense; most resources imply that conformity necessarily falls into fruition the next moment). If someone knows the origin of the "arising and ceasing" wording, I will be glad to hear that.

In "Path to Nibbana" (pg. 31-32) by Ajahn Jodok of Wat Mahathat (ven. Phra Dhamma Theerarach Mahamuni, also known as Nanasiddhi / Yanasiti etc; main teacher of Ajahn Tong Sirimangalo of Chom Tong):

Does this happen during 1st path review, 2nd path review, or 3rd path review. What are the instructions?
I did something rather similar to this and it ended well

Also, is this something you plan ahead for, such as a retreat?

Not only in review, but also in the first course. There are 12 exercises (as I see it the, ex 1 is for access concentration, then 1 per ñana, up to ex 12 for equanimity), then 3 determination exercises (13, 14, 15). Exercise 13 is a wish of clearer 3 characteristics ("May I be clearly aware of the coming-into-being and passing-away of all mental and physical phenomena appearing to the mind during twenty-four hours") , 14 is the one above.

Exercise 15 is for phala-samapati (extended fruition), wishing to attain "steady concentration" for 5 minutes, increasing the wish to 10, 15, ..., 1 hour, 2, 3, ... 24 hours (!) if it happens. "The number of minutes and hours is to be reckoned from the point of steady concentration with nonconsciousness onwards. In such a condition, we do not experience any feeling. The period wished for being fulfilled, consciousness will return of its own accord as in waking, but this is not waking."

See  this thread about some details how this is done in Chom Tong (which is similar). As far as I know, there is no discrimination about paths; similar to Mahasi, where you just do noting and let it take care of the paths.

Lots of repeated fruitions definitely a thing.

For me, fruitions are always very quick, <1 second, but they do vary.

Is there one for re-observation?

I once hit equanimity after/during 2nd path and rather than investigate, I got a job at a local retailer. Well, re-observation/desire for deliverance came into focus again, so I quit my job and drove down to a local Thai monastery. I started doing walking meditation in the parking lot. I interacted some with the monks, but mostly just trying to accept water, food as they were offered to me. I stayed out in the parking lot all night and eventuallly hit reobservation again due to physical fatigue. That was after getting rained on in the parking lot. These exercises that you mention sound a lot like what I was doing (the arising and ceasing of equanimity). It worked but I eventually dropped down into the lower ~nanas and stayed there for a long time. Now I am 3rd path going strong with periodic glimpses into 4th. I don't know if I will ever hit solid 4th path, because it is too hard to diagnose.

Edit. I might have also been seen as the recipient of a medicine buddha practice on the part of the monks, as I was accepting food and nourishment from them (not what you typically see?)

The exercise for re-observation is just to make a wish for patisankha, forget about the wish and continue with the practice

The insight stages in this particular lineage are technically related to the way of walking/sitting (such as how many sub-steps one does, in a more fine-grained way than for Mahasi, for instance), but that is just a teaching tool, as I understand it.