Plenty of reasons, why.
1/ They want to turn up at Waddington with 6 serviceable a/c and not having to leave broken a/c behind, 3 days gives plenty of time to sort out any issues.
2/ If it’s the Hellenic AF that may be hosting them, then they don’t tend to fly Friday or the weekend, so full facilities may not be available over these days.
3/ They may have used the opportunity to fly local DACT missions with the HAF, they enjoy very close relations.
4/ Because they wanted to.
Unfortunately my contact isn’t back on Crete until mid March, so he can’t confirm either way.