SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '83dea794afc2eac2d048037f350d8a8691e649a5917da60d017336dfc841a642' 
  AND token = 'MdYRSPRlpNSAlVlMN5dHx+lBf2EOTNnE5ZqU2Ay5noI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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