Either melted in the microwave then straight on fairly clean dry hair (no stylers), or blended with some cheap light CG conditioner (Inecto) and applied to co-washed damp hair or after a hydrolysed protein treatment has been rinsed off.
Chuck my hair in a shower cap, sometimes a turban towel on top to retain the heat of the head, leave overnight or even up to 24 hours. Sometimes the next day I take the cap off for an hour or two and leave the conditioner mix to partially 'dry' on my head, on the basis as water molecules leave my hair fatty acids might take their place. All depends on what commitments I have, what mood I am and how much help I think my hair needs.
If I used shampoo I would worry less about leaving so long, shampoo can lift the cuticle which can aid penetration at the point of washing out. And if I was not single I might be less willing to sleep in a shower cap!!
2a-2c, medium texture, porous/ colour treated. Three years CG, growing out mechanical and chemical damage = breakage and very high porosity. Past armpit length heading for waist.
CO-wash: Inecto coconut
Treatments: Komaza Matani, coconut oil, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss ultimate volume, Inecto argan
Styler: Umberto Giannini jelly, Boots Essentials gel
Experimenting with: going back to basics