There's 2 protein treatments I love. I leave them in from 5 minutes to half an hour, depending on how my hair feels... more or less every 2 weeks. I never use heat with them.
1) 2 or more parts moisturizing cheapie conditioner + 1 (part) egg yolk + 1 tablespoon olive oil mixed together: the yolk has a bit of protein, cholesterol, sulfur, other good stuff and has film forming properties... I don't like and I don't use the white as it's too much protein for me / I never use mayonnaise or egg powder for this reason. After this treatment I co-wash.
2) aubrey organics glycogen protein conditioner.