Do you have a magic number before it seems reasonable for two characters to feel like they are in love with each other? I always feel like characters are saying it too soon, or after not enough interactions, but on the other hand putting in too many of those moments may just feel like filler to get to that point of being in love. Do you have any suggestions?
It depends on the characters, just like how in real life it depends on the people. Some people do fall in love quickly while others take months or years to fall in love.
Perhaps read some romance novels and see how long it takes for other characters to fall in love? Perhaps some fall in love quickly and the plot revolves around other issues that are keeping them apart while other stories are about the characters slowly falling in love.