Minecraft wiki entry for Fishing, associated text: Each level of Lure enchantment on the fishing rod subtracts 5 seconds from the wait time.
If the bobber is not directly exposed to sun or moonlight, the wait time is approximately doubled (each tick has a 50% chance of not decrementing the count). For direct exposure, all blocks above the bobber must be transparent to sunlight, such as glass and tripwire, but not leaves.
If the bobber's block is being rained on, the wait time is reduced by about 20% (each tick has a 25% chance of counting down 2 instead of 1). The bobber must be located in a biome where it is currently raining and all blocks above it must not block movement (e.g. torch, tripwire).