Build time can be calculated from the Cost. For buildings that must be purchased with coins, divide the cost by 62.5 to get the build time in minutes. Ex: Sabertooth Diner 1,350 / 62.5 = 21.6 ==> 21m 36s
The Family Safari Lodges are by far the best return on your investment. It pays for itself in 21 collections which is almost as good as the Aquatic Infirmary which pays for itself at 20.5. The Lodges have a larger footprint(4x4 vs 2x2) so the Aquatic Infirmary is definitely the way to spend money until you start running out of Aquatic land.
The Sabertooth Diner has the best Earnings/hr but since it maxes out in 5 minutes the second best Family Safari Lodges makes more sense.