Therefore, I believe delaying investing in Bitcoin until we have discretionary funds is a bad idea. Time is ticking and can't be undone.
Don't you think you are getting it wrong here? That we should invest in bitcoin even when we have not figured out if we have a discretionary income to invest so i believe it's still ok to wait if there is no discretionary income to get started with.
The reason you should invest with your discretionary income is that things might not go as have plan it might go dip so if you invest with discretionary and such thing happens to occur you won't get your self up set because you investment with what you are afford to loss .