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[Artie]

Basically, going by length of enclosure, the absolute minimum would be halve the length of the snake, mind you I personally would prefer 2 thirds of the snakes size as minimum and don’t forget; they are arboreal and like the hight even more.
So 2 years, being a rough guess, would be maximum and it’s time to change.
It really depends how you feed, and how fast your Diamond grows.
As a general rule they don’t have heating 24/7 like other carpets, (maybe the first year) and don’t get fed every week (mine don’t anyway) and will therefore grow a bit slower.