at any one time, what´s the exact meaning , please?
The sentences says

At any one time 3 out of 4 people are on a diet.

Does it mean " once in a lifetime at least?

Thanks

Question

at any one time, what´s the exact meaning , please?
The sentences says

At any one time 3 out of 4 people are on  a diet.

Does it mean  " once in a lifetime  at least?

Thanks

Answer

No, it means that on any random week, day or hour three of every four people you meet will be on a diet.

Answer

Normally I would say this as:

At any given time, three out of four people are on a diet.  (This means "at any random time and date you choose".)

Answer

No, it means "at any point in time", or "anytime you ask the question of how many people are on a diet".

By way of example, imagine there are four people, called A, B, C and D.  
On Monday, A,B and C are on a diet.  
On Tuesday, A,B and D are on a diet. 
On Wednesday, B,C and D are on a diet. 
On Thursday, A, C and D are on a diet.

So each day, different people are on a diet.  It is not the same 3 people on a diet all the time.  But at whichever point in time  you ask the question: "how many people are on a diet?", you always get the answer: 3 out of 4.