First of all:
there are two methods of fishless cycling, one where you add ammonia daily, one where you add it once the readings have dropped down to 0. Both work, so it's entirely up to you.
I used the first method on my 15 and 19 (US) gallon tanks. I think I added 12 drops daily to the 15 gals (using a pipette from Boots), bringing the readings up to about 4 ppm. Once the ammonia dropped and the nitrites spiked, I added half the amount (6 drops every day). The cycle took me 14 days n this tank, 10 days on the 19 gals. Once it was completed (nitrites too had dropped to 0) I did a 70% water change to get rid of nitrates, and then added fish within 24 hours. Actually, I went on adding ammonia for a few extra days after the readings had dropped, but before the water change, as my other tank wasn't ready.