producing seeds

How long does it usually take for a plant to produce seed after you cross fertilize it? I was going to sell the plant/flower but it did not have any seeds yet. When I click on the plant it says "producing seeds" I just don't want to sell it then end up with no seeds.

Hmmm, it's been a long time...seed production might be tied into game speed and/or what level soil/water/flower/foliage you are on.
I do remember getting more seeds from higher tiered plants enriched by better soil/water/fertilizers farther into the game as opposed to beginner plants.