I'm leaving this here for info because I just tried to find the answer to this. It might be useful to someone at some point.
At about 6pm I gave DD 7.5ml of Calpol 6+. She went to her dance class and came back still feeling rough. DH didn't realise I'd given her medicine already and DD didn't know about the time limit, so she ended up having a further 5ml within two hours. I'm sure that sounds ridiculous to a medical type but it made me uneasy.
DH has spoken to NHS direct who will call back in a couple of hours and advise that since she hasn't had any more than that recently and isn't feeling sick she should be fine.
Tip: always communicate when you've given your kid some Calpol!