掲示板 Forums - いったん(一旦) or 一度?

One meaning of いったん is doing something temporarily for example: 一旦家に戻って、それからまた出かける。And one meaning of 一度 is doing something for the first time or doing something once in a specific period of time. But both of this words can be used as "once" in sentences like this: 一旦言い出したら、絶対に引かない。and also 一度言い出したら、絶対に引かない。Which means something like "once you say it you can't take it back." Is there any difference between those words regarding this meaning? Or can they be used interchangeably?

I'm not even sure if this question makes any sense

I see, thank you!