SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a103451642fa82b7858b4e43821be4c129206040ed836836682cedbf5a07982a' 
  AND token = '8WsdAMn+iSzWOKNdzP4zlmBl1XBNzWTzLZkXwemvIJE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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