I think that will vary from person to person, and which languages we're talking about.
I tried learning Spanish and French in parallel, and that didn't work out well for me because I kept tripping over the "similar, but different" thing. In the end I put French on hold. I had a brief go at Japanese in parallel with Spanish, and that worked OK (even though I had to stop Japanese because of time constraints).
I'm sure there are others (smarter people than me, or with a better knack for languages) who can handle the similarities well enough.
P.S.: What do you mean by "I don´t have much time left"?