There are some stats for this topic.... According to Hartl by the early Czechoslovakian Wolfdog 30% were in heat like dogs 2 times a year, 50 % like wolves 1 time a year. And 20% irregular. The numbers see to be the same (or similar) also now....
The lenght of the heat is by CLC very different. Some of the bitches you can cover already in 14-16 day of the heat and it lasts for about 21 days. Other are in heat more that 2..months and you can cover them for even 3 weeks (all the puppies are born on the same date of course
).