SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '912a03580fcae78f549f720f17f4de8e9666ce8816d9348fbfde54e813f15e4f' 
  AND token = 'OhUJgHynagjISwP3v7r/IVup6wJWRcaRuyshNfiLwPw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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