SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51a9b3b29d2a0e294fecf16f99e782512869e012a59db744301cba4549024127' 
  AND token = 'f2oQNG+Ymx7dDcyiYDMoBIr7zMqwlFbK83nCuEZgkcg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00036

JSON explain

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