It will depend on the part of the country you're in as germination will depend, inter alia, on daylight length and that applies particularly to marmite tree seeds. I am a member of the RHS and spoke to their help line on your behalf. ISTR you are north of the Watford Gap, so they tell me you'll need to sow seeds in as soon as the sun appears over the horizon and make sure they are in daylight for at least 16 hours for the first week after sowing. If the sun sets before sixteen hours are up, you could try shining a bright torch on the row until the seeds have been exposed to 16 hours of light. The RHS advisor says you may need gloves and a woolley hat and also an umbrella may come in handy.
HTH
