When does eu roaming add-on start?

[Herman]

I have a short upcoming trip to France when I will need use of my phone for data, texts and calls.  The online order page for 7 day eu roaming doesn't ask me when I would like the add-on to start.  So does it begin as soon as I hit the "buy" button or does it automatically kick in as soon as I arrive in France?

[MZone]

As soon as you use any data, send a text or make a call in a go roam area it will activate. 

[Herman]

That's great.  Thank you for responding.  Much appreciated.