Personally I would'nt sow them in seed trays but in pots, as they hate root disturbance, long thin pots are best ( you may be able to get purpose made ones from a good garden centre) plant the seeds in October, one or more seeds to a pot depending on size and overwinter in your green house or cold frame and plant out in or April.
Alternativly you can sow the seeds outside where they are to flower in march or April.
Ps, for improved germination soak the seeds overnight in tepid water. When the plants get to 4" (10cm)high nip out the growing tips for bushyer plants. Good Luck Tbird+