My gf needs advice about lenght of my first lockup

Hi, my gf needs advice about lenght of my first lockup- she doesnt want to be too cruel, but she was the one who came up with chastity play, and Im on board with it- the thing is, sex my 4.3 inch dick has been kinda frustrating for both of us, from the start of our relationship Im fisting her before penetration or using her huge 10 inch bbc dildo on her, because I just cannot feel enought friction to stay hard long, and as she gets wet, she doestn feel that much either- but she loves being stretched out, so most of the time she orgasms from my hand or the dildo stretching her and her fingering her clit, then I enter her, I cannot make myself cum because she is too wet and stretched for my tiny cock, and then she gives me handjob to make me cum. She recently wanted to measure me, and she fond out that Im kinda small, and then she laughted at me being kinda turned on but embarased about the whole situation. After that she started exploring orgasm denial with me, and then she sugested the cage. I bought one, it wits well, and now she needs some advice about how long should she have me locked. She feels like she doesnt want to be too cruel, but also feels like I dont really “deserve orgasm”, and I must say, that after watching her with her huge dildo I can see why she would think that. Thank you for your advice in advance! Get your own Orgasm Control toys: For men: http://www.amzn.to/1V6XQvv For women: https://ift.tt/1UWn54n