From my experience with deep learning I can eyeball it: one or two orders of magnitude. The fine details may be different on this particular problem.

In DL in general, if you have sort of equivalent CPU/GPUs (think a 5600 vs GeForce 3070) you'll find yourself in the range of 10 to 30x faster training with GPU. If you have substantially different platforms, you can start looking at 100x speedups or more.

For example, my mobile 4600H CPU trains about 100x slower than a desktop GeForce 2060. And close to 300x faster than the old Intel 7200u I use as a "slow system" to test things. Which also has a GeForce 940MX, that trains about 30x slower than the 2060 (if you manage to make your model small enough to fit in 2GB of VRAM).