It's the converters that only last a week - so that the Boost that they are offering for real money needs to be purchased again. There will be another one next week, maybe with different ratios and timers just to confuse things further.
The pumpkin collection goes on throughout the season, as indicated by the timer on the Carving Jacks item in the calendar.
Yes, I suppose they will change it to make players buy another booster, and maybe to change converters or make them harder, but the thing is I'm not sure the collected pumpkins will remain for next week, as right down in that event is the only place where total number of pumpkins appears. Just in case it happens I will change all pumpkins left for mistery landscape prizes before this event close on wednesday morning. I don't trust EA.
