I have always been just a day or two in leaving the silicon glue to seal and season. Imagine my shock a year or two back to discover that to really seal and structurally season the silicon (sorry there's a better word here) one should leave the silicon glue in a humid, warm spot for a week! In sealing a tank or whatever, a thin, consistent layer will form much stronger bond (ah, there the word, bond!) than a thick, goopy layer of silicon. My impatience is probably why a "fixed" aquarium would leak a year or two later!

Our speaker, a chemist and something of a practical engineer mentioned that his bosses were having a terrible time siliconing two small but important airplane parts together in a warm but very dry desert climate. He suggested a simple fix and was ignored until the other great minds had struggled for several days. They they took his advice and re-siliconed the parts together, set them on the hot concret, placed a bowl of water (for humidity) next to the parts and covered it all with something like a clean garbage can top (to hold the heat and humidity in there). After a week the new arrangement was everything they wanted!

He noted that the silicon would cease to be runny within an hour. Within a day it would be prtty hard. However it needs to absorb some atmospheric water and have a few more days to properly complete the chemical tranformation into a completely bonded silicon connection.

For your purposes of anchoring a plastic plant to a rock, the day or two is probably fine. But it occurs to me that any serious tank repair will be done during those hot, sticky July and August days.

Those rolled plants do sound intriging. What manufacturer and specific name do the have?