6.1 hours, where the tower is 50 mm on a side and follows a 60 mm model all the way up. That is frequently longer than the model it stands beside.
Multi-colour printing does not cost a bit more time. It routinely costs several times more.
The tower is only half of it
Beyond the tower itself, every tool change has its own overhead: retracting the old filament, feeding the new one, heating and purging, then priming back onto the part. Those seconds are spent per change, and a print that alternates colours on every layer racks up hundreds of them.
That is why the multiplier is driven by change count rather than by how much of each colour appears. A logo in one accent colour on a 300-layer print is not one colour change; it is potentially six hundred.
What reduces it
- Group colours by height. A model whose colours change at three heights costs three changes. The same model with colours interleaved throughout costs a change on every layer.
- Cap the tower. A model whose last colour change happens 20 mm off the plate does not need a tower carried to full height, and most slicers will let you stop it early.
- Purge into the part. Infill and internal solid regions can absorb purge, which removes the tower's plastic and much of its time. The purged material has to go somewhere; inside the part is better than beside it.
- Reduce the purge volume. The default is conservative. Light-to-dark changes need far less flushing than dark-to-light, and some slicers let you set the volume per colour pair.
The risk it introduces
A tall, narrow, solid tower is a collision target. If the nozzle catches it — and towers get knocked more often than parts, because they are printed to the same height with a smaller footprint — the whole plate is lost, including the model.
Anchoring the tower with a brim is worth the extra plastic on any print over about 100 mm tall.
The honest planning rule
For a multi-colour job, estimate the model, then estimate the tower as a separate part of similar footprint and identical height, and add them. That will get you far closer than doubling the single-colour figure.
A tower is a solid prism, so the print time estimator will time one from its base area and the print height. Its plastic bill is worked out separately in purge tower filament use.