SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50cff8dee9c9492e2a9741d7c937c23d1b53b4a215c1bd22076d60170131b673' 
  AND token = '/cdMtnbjs2IWIac4X+xQlU2N6jDKLtIRVGQcMYTjlAQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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