Slow start to wild ferment

[AnAppleADay]

Hi folks,
Usually do cultured yeast ferment with sulfited must but this time doing a trial run with wild ferment and no sulfites using home grown apples.
Approx 3.5 litres in a 5 litre carboy/demijohn with airlock fitted straight after pressing. No amendments to pH or acidity, but some nutrient added.
Ferment is slow to start, now into day 8 with just some stationary bubbles on top of must and no bubbling of airlock. Would this potentially just be because of the headspace in the carboy?
Have had it in a spot at around 17-18 degrees C but have recently moved to a spot at around 20-21 degrees to try and kick start the ferment.

Questions:
- should i pitch cultured yeast at this point?
- should i remove the airlock to oxygenate the must? Assume theres enough oxygen at present due to headspace
- should i leave it alone and give it more time. and if so, how much more time before pitching cultured?

Photos attached for context.

Thanks!

 

[lumpher]

Since it's an experiment, I'd let it ride and see what happens. It should be inoculated with wild yeast by now, so most likely it just needs time.

 

[AnAppleADay]

Since it's an experiment, I'd let it ride and see what happens. It should be inoculated with wild yeast by now, so most likely it just needs time.

Thanks. There is a slight increase in bubbles on the top of the must each day, so I assume it's doing something. No airlock bubbling yet, though.

My inclination is to leave it in a warm spot until the airlock starts bubbling consistently and then move it somewhere cooler for a slower ferment

 

[lumpher]

Wild ferments are usually very slow.