SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6d653b1f00e50533e835dcacbb13807f082b0fc588fe3b2b053e6d23b3f1fb93' 
  AND token = '8K147L9JtxwVkFZsAvLYXiCr/GAbcYQyMh9z+OB/6Hw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00037

JSON explain

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