JMeter Think Time - timer

Question

Apologies if this request is similar to others - I am new to JMeter and have searched for other relevants posts but couldn't find anything - or maybe I just didn't understand them!
I'm performance testing a system with a web based application. The front end system will be processing records submitted into the system via MQ - the front end allows the user to pick up a record from the queue, validate some detail, make changes and submit the changes.
There will be 20 users using the front end to do this message validation, update and submission.
Each user is expected to need 30 seconds to pick a message from queue, make changes and resubmit - so we are expecting 1 user to process 120 records/hour, so 20 users will be expected to process 2400 records/hour
The picking up the record off the queue, changing it and submitting the changes will be done via 3 individual web pages.
SO - think time across the 3 pages has been defined as 24 seconds (leaving 6 of the 30 second limit for rendering, server responses, db calls etc.)
However I don't know how to specify this within JMeter. From my reading I can see that I can add a Timer in as a parent to a sampler and I assume I can add a Timer in as a parent of the Recording Controller? - but I need to be able to specify that the 24 second think time is spread across those 3 different pages.
I read a post elsewhere suggesting that if I record using the proxy after adding the Gaussian Random Timer in as a child of the Test Plan (parent to everything else) then the http proxy will record the think time as a ${T} variable in the Gaussian Random Timer - I tried this and this didn't work (also I don't want to rely on this - I'd like to be able to understand and make changes to think time properly rather than relying on JMETER to do it for me.)
To reiterate - 20 users, 30 seconds for 1 user to complete a transaction, TT defined as 24 seconds - I am struggling what Timer to use, where to put it so that the think-time is spread across the samplers that equate to the GETS associated with the 3 pages the user will navigate through.
Apologies for the lengthy post - I just wanted to be clear and concise.
Many thanks in advance,

Answer 1

As per JMeter Timers documentation
Note that timers are processed before each sampler in the scope in which they are found; if there are several timers in the same scope, all the timers will be processed before each sampler.
Timers are only processed in conjunction with a sampler. A timer which is not in the same scope as a sampler will not be processed at all.
To apply a timer to a single sampler, add the timer as a child element of the sampler. The timer will be applied before the sampler is executed. To apply a timer after a sampler, either add it to the next sampler, or add it as the child of a Test Action Sampler.
Now regarding "what timer to use"
There are 2 scenarios:
Virtual-User-oriented scenario - when you try to simulate N users working together
Goal-Oriented-scenario - when you try to produce N hits per second load.
In case of scenario 1 even Constant Timer can be quite enough, besides it will provide repeatability of results. See above quote for information on where to put your timer(s)
In case of scenario 2 you'll need Constant Throughput Timer. If 20 users process 2400 records per hour and each record assumes 3 web page calls, it means that 7200 requests will be made in one hour which in its turn stands for 120 requests per minute (this is what you should enter into the timer's "throughput" area) or 2 requests per second.