PremierFella

No minimum period - to play it safe and make sure everything has switched correctly its usually advised to stay for a day or two at least when taking your number to another network via PAC code before trying to switch it again. What you propose will work fine (although most would probably rather use a dual SIM option if their phone allows as it doubles your chances of actually getting a workable phone signal at Glastonbury if you have two SIMs on different networks available!😀

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