You're using the wrong configuration element, go for Synchronizing Timer, add it as a child of the request 3 and set "Number of simulated users to group by" to 10
Also be aware that if you put a Timer at the same level as all requests it is executed before each request in its scope, each JMeter thread processes Samplers and stuff individually, if you want to run Request 4 with all 100 users - add the same Synchronizing Timer as its child and set "Number of simulated users to group by" to 100
More information: Using the JMeter Synchronizing Timer
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