Erysimums such as Bowles Mauve can be killed off when small if sown in autumn outside. If you can provide somewhere in a greenhouse (not heated) or under glass for them start them off earlier in the season. I have 3 cuttings on the balcony under glass until next spring, when I'll plant them out.
You might be getting confused with wallflower plants, sold in UK around October, which are planted out immediately for the following year - but they're plants, not seedlings.

It's like buying a packet of nuts with the warning 'This product may contain nuts'! Though to be serious, some parts of UK and maybe even Umbria, may have a sudden early or late sharp frost. I have always planted out my wallflowers in mid-summer so that by autumn they have nicely bushed out and in the spring will flower beautifully. They are fully winter hardy and a tough plant, but if in any doubt, and they have been propagated in a greenhouse environment then acclimatise them in degrees before you finally plant out just to protect any new growth. If the plant thinks its spring and is suddenly transplanted into winter, it might not do so well.

Just seen bamboo's response - thought erysimum was same as wall flower or are we at cross-purposes? Some are bedding plants but some are perrenials. They don't like a rich soil and will flower more abundantly if kept mean. Plant perrenials in spring/summer and bedding plants in autumn.

I think Bamboo was refering to the biennial ones sold as bare root plants just commonly called wallflowers as opposed to named perennial varieties like Bowles mauve, that if grown for seed will be susceptible to frost in their first year.
all my wall flowers [persian carpet] all died in the last winter, so not hardy enough for east yorks :o(

Yes, I was a little perplexed by your response, too, Bamboo, until I realised that I was referring to what I used to call Cheiranthus - i.e. biennial wallflowers, but had understood that these days goes by the name of Erysimum. Presumably you thought I was talking about perennial wallflowers (Erysimum, too, I think?). Yes, you are right. I have the seed, what I need to find out is a) when am I supposed to sow them, b) how long does it get to the plant stage that are sold around October time in the UK, and c) what do I need to do to get safely from a to b?
Avkq, our frosts are pretty much guaranteed over by the end of April, and winters tend to descend late but suddenly and rather fiercely up here in the mountains compared to the UK. I hadn't appreciated wallflowers liked poor soils, and had planned on planting quite big tubs with them for spring flowering. In which case, do you have any advice as to the best soil/compost to put into those tubs?

Hang on, I'm even more confused - you say your seeds are, as I thought, the perennial variety, but then refer to the ones sold in October in UK, which aren't perennial.
The biennial ones sold here in October are called the common wallflower, proper name Erysimum cheiri. I'm assuming that's NOT what you've got as seed there.
The others are perennial ('Bowles Mauve', E. 'Bredon', E. 'Butterscotch' for instance).
If I'm right in my assumption that you have a perennial seed there, then the instructions given under my first answer apply.

No, sorry, Bamboo, I've just re-read my response and I haven't made myself at all clear. What I have are the biennial seeds, Not the perennials.

Ah, well then follow the instructions you have on the packet - they should be small to medium plants by October next year, which is when you plant them out ready for flowering in 2013.

I have bi-ennial wallflowers growing in the tiny crack between my drive and neighbour's fence! Follow instructions, as bamboo says, but plant out sooner than October, in july or august, and water well initially, as they will then bush out more and flower better in the spring. Also found that those I potted on into larger pots before planting out in summer, bushed out quicker and better. Those I planted straight out (the second lot) are still only single stemmers.

Not sure I agree with that Avkg47 - there's a reason why they're sold in bare root bundles in September wrapped in paper - the rougher you treat them, the more flowers you get....