SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6c804c034900bb1bd42c04d6e75bfece002c090124c670ba81bf2a5873b74397' 
  AND token = 'DjMQtMTSQOgTVRi99tSZZABk5CbRVUjiD4aeuDwccyE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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