If I attain a 60-day double entry visa, remain in the kingdom for 3 months (60 days + 30 day extension) and then exit the kingdom, how long do I have before my second entry is null and void?  Does the 6 month clock reset?

 

My plan is to stay here in December, January and February, and then depart to Nepal for four months.  So I would return to use my second 60-day entry on or about July 1st.

 

Feasible?   

The visa itself has a validity date on it. Normally 3 or 6 months from date of issuance.

 

All entries must be made before the visa itself expires, making your plan not feasible. Better to get a single entry tourist visa and once you plan to return for the second time to Thailand get another tourist visa, depending on how long you intend to stay.

Visas issued in SEA are valid for a period of three month, in case of a double entry you must use both entries within that three month. 

 

Visa issued in US,Canada, Europe, Aus are usually valid for 6 month, so your plan might work.

 

He plans to stay 3 months in Thailand and than go for 4 months to Nepal before comming back. So he will make his second entries 7 months after he gets the visa.