Waiting period between visit visas for parents

Hi..
Can anyone tell me what is the waiting period for visit visa. My in-laws are in visit for 3 months extended one month. Once they exit how long does it take to take another visit visa. I appreciate your time and response.

Prini

Hi there,

Did you get a response for your query. I am told its 6 months between the 2 visas , please respond.

Thanks
Ruth