Well wait til you can convert. Otherwise you lose plunder. If you have 525 bil lying around go ahead and convert Aug 15
T4s price will be cut which i presume you would lose 80% of their return value if you wait (4b return on a t4 l3, when now would be about 20b)
Sorry to burst your bubble pat, but you get 5B for lvl 3 tier 4 when dropping. You only get 20% of your money back when dropping building. You would get lil over 2.5B as of next week
It's really basic here folks. If you have the gold to convert then make sure you sell prior to price reduction. If you can't afford to convert then if suggest taking the 2.5 bil extra loss as you stand to make more gold having a t4 lvl 3 while waiting for the gold to build t5 rather than having an empty land. As for when... That's personal pref but since torture garden and the hatchery are both slightly weaker than t4 l3 buildings it will cause a reduction in your ally plunder accordingly. However the colony is a slight increase and therefore creates a slight plunder increase.