Is January the time to start them - are they like geranium seeds that they require that much lead time before setting out?

Are the yellow and purple as fragrant as the white (a friend grew the single white, it had a pretty fragrance).

I 'pre-germinate' some of my seed using the baggie method with coffee filters (read somewhere that paper towelling wrecks fine root hairs when trying to peel off, coffee filters do not). I always popped open the bag a few minutes each day to refresh the air inside and check for germination. One year I decided to use bottled spring water thinking that would be better for the seeds (one with chlorinated tap water, one with the bottled). The bottled ones went moldy within 4 or 5 days! The ones with chlorinated water sprouted. These were my Spanish 'candy' onion seeds. I didn't want to plant one seed per soil cell, and then end up with some cells being empty, nor did I want to use 2 seeds per cell because then some cells had 2 plants, others had none.

Sorry - gone off topic. Thanks for sharing your datura germinating experience!

Last year I started the daturas at the end of Feb. This year I'm starting them for the market garden sales so I want them a bit bigger. Last year, from Feb. sowing, they were about 7" tall when I planted them out. Marg

Daturas would be classified in my book as "easy". In fact after intentionally planting them in my yard a few years ago, they now self sow and must be weeded out to be controlled. Are you using bottom heat to germinate the seeds? Datura loves warmth. They usually sprout in just a few days for me. If you collected the seeds, try giving them a cold treatment for a couple weeks in the fridge before putting them on heat. (This helps break dormancy) Not all seeds require this, but I make it a practice with any collected seeds to up my success rate.
Once a datura spouts, it grows fast. Starting now should give you a large foot tall plant (or more)(which would require re-potting for sure) by spring. Personally, I would wait until mid-March.

Yes, little roots grow quickly into a paper towel. If this happens, instead of trying to pull them out, it's best to just cut the towel and plant the root with the little piece of paper stuck to them. (hard to do if they are all tangled together) I hate using coffee filters because of their shape makes them too cumbersome for me. I use a paper towel folded in half and then lay a strip of newspaper on the bottom half. That way you have the water-holding and air-allowing capacity of the paper towel, but the roots won't penetrate the newspaper as readily. (No, the ink doesn't seem to bother the seeds at all, although it makes it harder to see them, so I use plain newsprint.)