SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51d04adc6adc93225de2272f601cb9fc2a288b3555e8b5864a105646fa417211' 
  AND token = 'FNfAFWQXEm/Uz/f3dDFLwtTZTp8JSRg3YtNXqOmJjzY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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