So, I did the math and found out this is doable. I currently have 140 dragons that are able to go to level 20. There are probably another 10 or 15 more to get. I estimate that if I did nothing but feed dragons for 2-3 years, I'd get 140 dragons to level 20, no problem. So why not make it a goal and document the journey?
So my start date will be Sept 14, 2015, which was the 1 year anniversary of the start of building my current park. I started with 140 dragons at level 17 and zero dragons at level 18. In one week I fed 11 dragons to level 18. So I figured it will roughly take 15 weeks to get them all to level 18. That's close to January 1, 2016. Let's say 4 months to level 18. Then I estimated it will take twice as long to go from level 18 to level 19 (8 months). And from there, twice as long to go from level 19 to level 20 (16 months). That's 4+8+16=28 months. Give or take some months, since I still don't have all the dragons and they will be adding more to the mix. I hope there are no plans for adding another set of elements, because that would totally screw this up.
There aren't too many places to blow cash right now, so what else do I need to spend coins on? I'm lacking one of the 2 billion coin islands, but I'm in no hurry for that.
I will probably update once every two months.
So here we go:
Sept. 14, 2015
140 dragons at level 17
0 dragons at level 18