SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a121ee7c746c234442306109712218ddb47bedebe6022fd2140043fe3b190742' 
  AND token = 'ISz7yhvNsRGIUuraHSGbjq5Dvqa2ZTP9MkEpAzMKEeA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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