SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '52acf6a02beb0d8c6d0881b399689dd57a40269d16688881900271076908acdc' 
  AND token = 'u14tRd7SVTsZvrB8o/x4NMVcpYcFmmZiJFScOn2HBY4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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