Maaseh Rav Siman 35
Can copy this into an AI, or connect the whole library to your assistant. For deeper learning, you can directly use the original seforim, sites, and apps.
יש לענות אמן כששומע הברכה אפי' אחר יוצר אור באיזה אמן שירצה חוץ לאחר שפתח בשירה חדשה:
Sefaria Community Translation
One is able to answer 'Amen' when he hears the blessing even after 'Yotzer Ohr' to whichever 'Amen' he desires except for after 'Shira Chadasha' (prior to Shemonah Esrei) is begun.