I really can't say...
Your initial query was whether you should be concerned and that was easy to answer.
Without knowing the method of construction, the actual condition of the rudder, etc., etc., it is impossible for someone to give you a meaningful answer.
In the worst case scenario, one day could conceivably delaminate the entire side of a rudder. Odds are really high against that happening, but I've actually seen it happen on crummy rudder, in poor condition, with dark bottom paint, in July, here in the South. A well made rudder with no issues and left partially shaded will not be likely to have any problems result in only a week.
If it were mine and I couldn't get back to it, I would call someone and ask them to throw a tarp or sheet of plywood over it untul I could get back.
Then - No worries Mon!