The wiki may be misleading as about 1/4 of all my serpant encounters have occured during the daytime (calm full sunlight day). Their respawn rate might be similar to that of a blue troll in the forest - they won't spawn in the same location the very next day, there will be multiple days required before you want to check the same area again - and... a bit of luck, but I have also learned to sail at medium to low speed as to not accidently bypass chance encounters that haven't rendered properly on screen yet.