How long are they going to run?

[tufguy]

1) How long are they going to run?

It means we are asking what distance are they going to cover running. Am I correct?

2) How long are they going to run for?

It means we are asking how much time will they run for. Is it correct?

 

[GoesStation]

Both questions are asking for the length of time they're going to run. If you want to know the distance they're going to cover, you'd ask how far they were going to run.

 

[tedmc]

Or
What distance are they going to run?

 

[Phaedrus]

Interestingly, "How long is the run?" can be used to ask about the time or about the distance of a planned run.

A: How long is the run?
B: Five miles.

A: How long is the run?
B: About forty-five minutes.