What's a good time to set to be locked without a orgasm.

With regard to health and safety, there is no actual proven medical proof that you need to orgasm.
As Jules mentioned it's entirely down to comfort hygiene and practicality. If it's a quality open caged style metal device and it doesn't pinch or chaff then there is no reason why can't be worn indefinitely and if this is the case then the decision should be hers.

 

However if it's the one featured in your avatar then I would recommend investing in something made to measure unless you have a particularly high pain threshold or very tough skin..
You'll find that the bottom end products are often prone to rusting or chrome poisoning.
BTW (at tip for you) if you are in pursuit of her pleasure you may wish to consider removing your socks in bed.

 

Based on every survey I have seen on websites dealing with male chastity, it would be 30 days. I know of one custom device maker who gets one orgasm a month. I get one whenever my wife thinks further denial is affecting my well being. Chastity does not really start until you want it to end. Being denied an orgasm when you can stand it, is just waiting. I learned the difference. Yesterday I told my wife needed an orgasm and she told me that I only think I do and to hang in there.