These are the balsamina type and like warmth. I live in an area that has enough warmth for the normal bizzy-lizzy type to survive for years, this type has already died back. They take more sun than the others. so around April 1st, surface sow and don't cover (they need light to germinate) and keep at about 27*C. for about 10 days. Reduce temperaure to around 16*C and grow before planting out. Welcome to GoY!

I found a trick to growing I. balsamina seeds:

Look for small translucent pebbles (quartz or marble, about 1/2 cm across) or chips of glass. Make holes in the soil with a pencil tip, drop the seed in, and cover the hole with a chip or pebble. The seed sprouts very quickly, pushes off the roof of its "greenhouse" and rapidly adapts to the local environment. True, it's finicky work, but I get bull strong plants, really fast, without having to harden off.