请问伦敦Oyster Card有规定要用几天才可退卡吗？退

can be refunded without problem.
sometimes, bad ticket office guys may refuse by various excuses, such as 'oh, sorry, the machine does not work so I cannot do if for you now.'

用完就可以马上退，余额连押金一起

余额押金一起退，没有限定几天退卡

tfl.gov.uk 看下吧

一起退，很方便

当场就可以退！

什么时候退都行 一起退

当场就可以退！