SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '76c7d5b44ad684c5331e1102c003882316efe01bd7170da0f7c6d2b3f7dfe256' 
  AND token = '5RTsKcasWUr50VWvBUWN8PjR+gqEIRRscIw4EwIpA80=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00017

JSON explain

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