There will be a time difference due to A/D conversion and then D/A conversion.
A small time difference won't bother me. And I'd be practicing individual words or short phrases so it should be negligible anyhow.
And, you hear yourself while speaking - you expect to hear a difference by playback during recording?
I don't know about you, but to me there's a massive difference between how I hear my voice as I speak it, and how it sounds when it is played back to me. I actually couldn't even recognize my voice as being my own the first time I heard it recorded. So, that'd have to be a yes, I do expect to hear a difference, as long as I turn up the earphones high enough to carry over the 'real' voice.
[Edit]
Probably the best you can do is to either get sound-blocking headphones or simply use earbuds and some hearing protection cups on top of them.
That's exactly what I want to do, just need to know how to get the actual sound to them as I'm speaking it. And it seems you've just solved that for me, so thanks
Also, I don't need it to be exact, I just need to be getting some sort of reference to work with as I'm practising, and I think this will be good enough for that.