Rebun-Rishiri advice

May 28 morning ferry 06:40 to Rebun island; join bus tour 08:40 ; take 13:25 ferry to Rishiri island ; last ferry to Wakkanai 16:40

Could anyone please advise if the above itinerary is worth pursuing?
Any other advice is much appreciated.

I have only 3 days for this trip; departing May 27th from Sapporo by train and returning to Sapporo by 29th also by train.
I would like to join the bus tours for both islands, unfortunately my timing is out. According to the Soyabus' timetable there won't be afternoon tour until 1st of June.
http://www.soyabus.co.jp/teikan.htm

If I opt for staying one night in Rishiri and take the morning tour on the 29th, I will definitely miss the 17:00 train ( last train) for Sapporo.
http://www.heartlandferry.jp/english/index2-1.html

If I only had three days, I would not do Rishiri and Rebun. It takes at least five hours to get to Wakkanai, another five to get to Sapporo, and including the time of the ferries, you are looking at a total about fourteen hours (a whole day).

Also, if I remember correctly, a large majority of the flowers on Rebun don't start blooming until sometime in June. You should be able to see some flowers, but to devout such a large amount of time to getting there without even seeing the island in its full glory seems a little off to me.

Others may disagree with me, but I do not like the two islands as a day trip. One of the best parts of my trip was spending the day biking around the entirety of Rishiri. They are very slow places when compared to Tokyo, and I feel that they should be enjoyed as such.

if I remember correctly, a large majority of the flowers on Rebun don't start blooming until sometime in June.

Ben,
Thank you for your speedy response.
My timing for this trip is all wrong, could be better as you said if my visit was in June, unfortunately I have to be in Tokyo by June 1st. I am seriously reconsidering the trip, may put this off again for another time.