dude, if they are autoflower you do not need to switch the light. put the seed in the soil, water when the soil is fully dry; best to leave the light from the beginning either 24h on or 20h on 4h off (examples of commonly used light schedules for auto plants) if you give less light, they will finish, but will be smaller.
Signs of flowering are pistils, the white hairs, so look for them... timing varies depending on the strain and pheno you have. From 2-7 weeks +/- they'll stay in vegetative stage then they will automatically start flowering.
good luck!