When should we register a trademark?

Yes, for the U.S. The USPTO will not register your mark until you can show use of it. However, the U.S. does permit filing what is known as an "intent to use" application which provides a priority date as early as the application filing date once use has been demonstrated and the mark has registered. The requirement to demonstrate that use can be postponed/extended for 3 years from the date the application is allowed to register by the USPTO which is roughly about 6 - 12 months from the filing date of the application. Thus, if you are worried about a competitor rushing to use or file an application to register their similar mark, you can file the application to register your mark as long as you can foresee using the mark and offering the product within about 3 or 3.5 years from the application filing date.