Well, my research says its ~14 days to root, and then 6 weeks to flower, depending on the variety. I'm not sure how much time topping adds. No hands on experience here, just based on my I-research.

Cheers,
Russ

Cuttings will take 3-4 weeks to root, they then need 4-5 weeks 'potted on' in 3 1/2 or 4 inch pots to establish strong roots and growth before planting out. Then reckon on 4-5 weeks to the first blooms. I'll be planting mine out at the end of May and expect the first blooms in the first half of July with the main cropping through August and September with blooms continuing until November or the first frost, whichever comes first!

Here is a link that might be useful: Withypitts Dahlias