SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '596ac61943720f137d1145d58b84f833f73d621504fb24d7069cc5d91646d93f' 
  AND token = '5tABYkqgRtTYexS5+GEvO8IjJacF8mhxm0xcziD4vD0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}