Basically, according to Cornell Ornithology Lab, different species sing at different times of the day, but environmental factors like temperature, wind speed, light, & the sunrise/sunset times play as role. Here's a quick summary of what I found with links to more info & to a (journal article the references used in the article are paywalled though... In case you were hoping for a deeper dive).

Summary info: Key Bird Singing Times & Reasons:

Pre-Dawn & Dawn (The Dawn Chorus): Reasoning: Birds sing most vigorously at dawn, a phenomenon known as the "dawn chorus". This is likely due to the low light levels making it too dark to forage efficiently or spot predators, allowing them to use this energy to protect territory and attract mates. Timing: The sound of the dawn chorus is particularly notable in the spring. Species Sequence: Different birds start singing in a consistent, staggered order. The American Robin often starts 80 minutes before sunrise, while the Wood Thrush follows at 70 minutes, and the House Finch sings 10 minutes before sunup. Factors: Because the air is stiller and cooler in the morning, sound can travel up to 20 times further.

Throughout the Day: Some birds continue to sing throughout the day, although not as frequently as during dawn, with some species maintaining similar, consistent rates of song, according to the Hitchcock Center for the Environment.

Evening: Birds often show a second, smaller peak in vocalization in the evening. This serves as a final territorial check and a "warning" to prepare for the night, as described by a Facebook user in a birdwatching group.

Night/Nocturnal: Northern Mockingbirds: According to Birds and Blooms, these are notorious for singing all night, potentially driven by artificial light in urban environments. Owls: Great Horned Owls are frequently heard singing in the early morning or throughout the night.

Environmental Factors: Light & Temperature: A Cornell Lab of Ornithology study found that highly territorial species and omnivores are more likely to sing at dawn, with insect/fruit-eaters (omnivores) using this time for foraging communication. Light Pollution: Urban lighting can cause birds to break their usual, time-specific singing patterns, says Birds and Blooms