Since basically everyone and their mother in Star Wars who has a Lightsaber can react to / block blaster fire, I figured it should be useful to figure out how fast these laser blasts actually are.
inb4, they are Subsonic because they seem slow in the movies.
Jokes aside, their speed isn't very consistent via statements, but we have to work with what we got:
- He dived into the street. He rolled, coming up to slam her hip joint with his shoulder. The impact folded her over him; he lifted her, turned, and sprang back for the corner. Bright flares of blaster bolts bracketed invisible sizzles and finger snaps of hypersonic slugs.
- Source: Shatterpoint
Slugthrowers are explicitly described as being hypersonic (At least Mach 5), and Slugs are projectile-based weaponry that are completely obsolete in the Star Wars universe. So Blasters should at least be faster than Mach 5.
According to this calculation, a Blaster Bolt moves at 2,217.356 m/s or Mach 6.516. Pretty consistent with the Hypersonic slugs.
- Like most energy weapons, turbolasers fire invisible energy beams at lightspeed. The 'bolt effect' seen when a turbolaser is fired is actually a glowing pulse that travels along the beam at less than lightspeed.
- Source: Fact File 47
Turbolasers are described as firing energy beams at the speed of light, like "most energy weapons".
- Energy weapons fire invisible energy beams at lightspeed. The visible "bolt" is a glowing pulse that travels along the beam at less than lightspeed (...) The light given off by visible bolts depletes the overall energy content of a beam, limiting its range. Turbolasers gain a longer range by spinning the energy beam, which reduces waste glow.
- Source: Star Wars: Attack of the Clones Incredible Cross-Sections
Another statement that energy weapons fire invisible beams at the speed of light.
- As though it in turn sensed his contact, the floating remote droid let loose a volley of laser beams aimed at him, simultaneously zipping from one midair position to the next as it fired. Jax, blindfolded, whipped up the energy sword, countering each burst by knowning, before it was fired, which direction it would come from. One...two...three...four...five...
- The sixth, and last, beam stung him painfully on the right side.
- "Blast!" Jax pulled off the blindfold and spoke the deactivation code for the remote, which drifted to the floor. He sat down on the extruded lip of a wall couch and looked ruefully at the weapon in his hand.
- "I see its remote one, human zero, " a voiced said. Jax looked up to see I-Five in the doorway of the small, enclosed courtyard in which the Jedi had been practicing.
- "I'm beginning to think that Laranth is right, " Jax said. " The Jedi should have practiced more with other weapons. " He grimaced. "Don't tell her I said that."
- "On the other hand, no one but a Jedi could have blocked five out of six beams. "
- Jax shrugged. "It makes no difference if it's the sixth one or the first one that kills you. Dead is dead. "
- "I wouldn't know. I do know, however, ", I-Five said, "that you're much better with that sword than you think you are. "
- Jax glanced down at the weapon, saw his disorted reflection looking back at him from the blade's surface. "Yeah? How do you know th---?"
- I-Five suddenly whipped up his left hand, index finger extended, and fired a laser beam at Jax. The beam splashed off the ionized fire that suddenly coated the length of the blade, which Jax had automatically raised to block the beam.
- "That's how," I-Five said, "The speed of light is just under three hundred thousand kilometers per second. You are currently seven-point-three meters from me. Your Force-augmented anticipatory reflex action is obviously working fine. You just have to let it."
- Source: Star Wars: Coruscant Nights II - Street of Shadows
This is probably the most explicit and well-developed statement that blaster bolts move at the speed of light.
- He triggered the first pair of concussion missiles, knowing that, unlike the laser cannon, they did not strike at the speed of light.
- Source: The New Jedi Order: Destiny's Way
This is referring to the Milennium Falcon's laser cannons, explicitly describing them as being fired at the speed of light.
- Though the transparisteel in the doors at the end of the main hall he could see distant flashes, narrow red streaks heading one way at the speed of light
- Source: The New Jedi Order: Enemy Lines II - Rebel Stand
- Sophisticated sensor algorithms compressed the combat that sprawled throughout the galactic capital's orbit to a view the naked eye could enjoy: Cruisers hundreds of kilometers apart, exchanging fire at near light-speed
- Source: Revenge of the Sith Novelization
Another description stating that Turbolasers fire blasts at near the speed of light.
- He had the Force to guide him through, and the tri-fighter had only its electronic reflexes—but those electronic reflexes operated at roughly the speed of light. It stayed on his tail as if he were dragging it by a tow cable.
- Source: Revenge of the Sith Novelization
Not completely related, but tri-fighters are capable of reacting at roughly the speed of light. Felt like bringing that up, since they are random droids.
- "The wave of charged particles blew over her at lightspeed, nearly - but not quite - generating enough static to drown out Gavin's fierce cry of exultation."
- Source: The New Jedi Order: Edge of Victory - Book II
Blaster Bolts are almost certainly to be Lightspeed, at least in the Legends Continuity. There are so many blatant statements it cannot be ignored. Energy weapons such as Turbolasers are also repeatedly stated to be Lightspeed, even in the Disney Canon.
Even at their slowest, most downplayed speeds, Blaster Bolts should be faster than the Hypersonic Slugthrowers.
This means that Han Solo can react at Lightspeed.