There is a timer function, which in the middle of its work should call the http triggered (post request) function. How to do it? Will Durable function - chaining pattern help? How to pass parameters (in requestBody) to the called function? p.s. I apologize if I expressed myself illiterately in this matter.
Investigated the implementation of the chaining pattern. In the examples there was only a function of type Activity Trigger.

How to do it? - You will submit a WebRequest from the timer triggered function to the http triggered function.
Will Durable function - chaining pattern help? - Probably not, nothing you have mentioned so far in your problem statement leads me to believe that changing your pattern will address any of your concerns.
How to pass parameters (in requestBody) to the called function? - The documentation for webrequest provides some examples