We move according to the horse. Gavotte was long lined for about a month, 3 days a week, then we hooked a pair of ATV(small) tires to the traces, and when she was comfotable with them on all surfaces, maybe 4 times, we hooked her to the drag, which was not much more than a sturdy pallet, because it was fairly rotted. One day we let her drag that, then 2 days later we put a 5 year old on an upside down plant bucket, then Mike on the bucket, then me. Then the next week we hitched her to my marathon carriage, in the cutting pen first, then the next day Mike drove her out into his field, around round bales, cones, everything.
More time drilling is not neccessarily better, just more boring. When the horse masters the lesson, move on. Let them make mistakes, get traces around their legs, twist and untwist, so they learn not to panic.
Everytime I hooked up to something, the first thing I did was let the horse take ONE step, then stop, so they learn that WHOA makes everything better, and I can fix it, instead of turning it into a panic or bolt. Draft people train them the opposite of my light horses. They hook to something heavy first, and with the light horses, we always work our way up in weight.