If they grow at a consistent rate, then ((22 x7)/18) x 5 should be the length of time to get to the 23 grams target shouldn't it?
Breakdown:
22 weeks to get to 18 grams
Therefore 22 x 7 = 154 days to get to 18 grams
154/18 = 8.56 days per gram
Therefore an additional 5 grams will be 8.56 x 5 = 42.8 days or approx 6 weeks hence.
Quite assumptive I know and if incorrect in terms of growth being consistent, do feel free to contribute.
Point being, by this calculation, Harvest weight is 6 weeks away, or Monday 18th March (approx).
BTW Full article won't open as need to be a paying subscriber.