I have been cycling for 2 weeks now and the ammonia is processing in at least 24 hours.
For 2 days now the nitrate test has been going purple as soon as it hits the water,i presume this means off the scale,and it ends up a weird greeny purple colour.But today when i tested the water the ammonia is about .50.I will just carry on bringing it up to 3 or 4 but a bit perplexed as to why the ammonia hasnt fully gone this morning.
I can't offer an explanation, but can say you're not alone.
I'm currently cycling two tanks, and one of them (240l, heavily planted) has shown the same as you recently - no idea why.
On the plus side, as of last night, both tanks seem to have finished cycling at the same time - it's fish time!