amboss flow chart “Evaluation of palpable breast masses” actually has reexamine 3-10 days after onset of menstruation here
Dynamed: 'For women < 30 years old, obtain ultrasound of breast (Strong recommendation), followed by mammography for suspicious lesions (Strong recommendation). For women < 30 years old with a dominant mass and a low clinical suspicion of breast cancer, observation for 1-2 menstrual cycles is an option prior to ultrasound. ’