Can a soul stay between lives indefinitely?

When we talk about "indefinitely," this implies that spirit time works on human, linear time, but it doesn't. If you're asking whether a soul can choose to not reincarnate immediately, using our typical timing, then yes; however, all time is happening at once, so staying between lives indefinitely is placing human time over top of spirit time. We can't truly know how long forever is, because it's all happening at once.