Multiple people have reported that they have received their invitations to confirgure their Model 3, marking the first time non-employees have been able to order their car. Lead time looks to be just under four weeks.

Tesla Model 3 invitation

Below are screenshots of the configurator. 

Tesla Model 3 Configurator Design Studio
Tesla Model 3 Configurator Design Studio
Tesla Model 3 Configurator Design Studio
Tesla Model 3 Configurator Design Studio