> This is not yet possible with httrack - but I will 
> implement in the near future

Well, the future is definitely near.

Download the current 3.33-beta-2 release, the option is now 
implemented as the "Number of connection per second" 
accepts decimal values.

In your case, 10 hits / min == 10 hits / 60 sec == 0.16 
hits/second. Hence, enter 0.16 as number of connection per 
second. (ONLY starting from 3.33-beta-2 - it will NOT work 
on previous releases!)