SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a51a5477744b3278a0034a4ea090623e7da140113283438c363735f32af34326' 
  AND token = 'rkYVXhCItjbcSsu0Hfzy1aNOxBlD6d17uVSV+3tRddg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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