This is because of UL listing requirements.
Under normal pressures the pipe joint compounds does not need a curing time. If the pressure in the lines is 125psi or higher, the recommended cure time is 4 hours before initiating pressure. Call Oatey Customer Service when in doubt.
Oatey does not have any products that will work in this application.
All joint compounds with the exception of Megaloc will not be removed easily. You should check with the materials manufacture that you are removing the pipe joint compound from first, to confirm what cleaning chemicals are compatible with their product.  Start by trying to remove the pipe joint compound with white vinegar and working your way up to acetone. Remember to always test a small out of sight area first, before damaging the finishes or affecting the integrity of materials that the pipe joint compound was adhered to. Megaloc can however be cleaned off hands and tools with a dry rag, and easily washes out of cloths with soap and water. 
All ½”, ¾” and 1” wide tapes are installed the same way. After you select the proper size of tape for your thread, you will wrap in a clockwise motion, while keeping the tape at the bottom of the thread. For ½”, ¾” and 1” pipe threads you will only need to wrap the threads in a straight pattern 3 to 5 times around the male thread, if the tape width is the same size as pipe diameter. For 1¼” pipe threads and above or when tape width is smaller than pipe size, you will wrap 4 to 5 times starting at the end of threads and working up.     
The following Oatey pipe joint compound products are approved for use in this application: Oatey Great Blue, Hercules Block, Hercules Grrip, Hercules Megaloc, Hercules Pipe Joint Compound, Hercules Pro Dope or Hercules Real-Tuff are all safe for this application. 
The following Oatey pipe joint compound products are approved for use in this application: Oatey Great Blue, Hercules Block, Hercules Megaloc, Hercules Grrip and Hercules Real Tuff. 
There are no limitations on the diameter of the pipe. You should always wrap the tape enough times around the male threads in order to fill the spigot (female threads). Any pipe sizes over 1¼” with pressure and fluids moving through it should have the male threads wrapped with tape and then the approved pipe joint compound spread over the tape.
Yes. Mega Bubble will help you locate any non-liquid leaks and will not compromise the pipe / fitting materials.    
Yes. All Oatey thread sealant tapes will work on natural gas lines. Oatey does however recommend the use of yellow gas line thread tape with PTFE on all natural gas line installations, product #31403. The Oatey yellow gas line thread tape is approved by code for this application and the yellow color is a visual identifier that the correct tape was used in the application.