Optimal timing to change my last name I am a third year PhD student in a US business school. A this moment I have a couple publications in a totally unrelated field which are not important for my career. Regarding my PhD research, I just submitted my first paper in my field to a journal (we haven't received a response yet). This submission was done using my complete legal name. I have also done a conference presentation using my whole legal name and I have been accepted for at least 1 more in the next few months.

I happen to have a 4-word last name (two Spanish last names, one of which is compound) and I was thinking of shortening it (as I have found it is difficult to pronounce and confusing for most people in my field and there is always some issue locating my badge, etc.). My idea was to contract my first surname (the compound) into an initial, like a middle name, so I would be "Name S. Lastname". I am not thinking about changing my legal name, only using this contraction in my publications, conferences, etc.

Is it too late if I have already presented in conferences and have one submission (not publication)? Is there any social perception that name change is bad? Is there a way of making this name change effective in this first paper submission (i.e., when it comes back for revision, submit it back with my new name), or once submitted it is too late? Will it be a problem to use a name as a researcher that is not my whole legal name? Will it have an impact in the job market?

Thank you.
Lots of people publish under things that aren't their legal name (nicknames, middle name, one last name instead of two), and I've never heard of it being a problem for anyone.  As for the timing, in all the cases I'm familiar with (and other fields may be different from math), there's a time after acceptance where you can make minor revisions and I think it shouldn't be a problem to modify the name you're using then.