The seeds prefer warm to hot conditions to germinate. Usually, I sow them in a covered container and leave them under bright shade. Not all but the first few will germinate within a week.
B. liniflora does best during the hot and dry season here so I sow my seeds in March and by June-July, they start flowering and produce a lot of seeds. Each year, I collect the seeds to sow the following year i.e seeds are usually a year old. The best germination rates I've got is prior soaking with 1% bleach.