SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a51b5b5294a053a869b998b668081919232272e6b03288f05d8635dbbbac85be' 
  AND token = 'NxmjJINTEFTpSV3qqKXXLw9OXRBreW3T2y3iHMT31cQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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