If it is the right kind of job, it will help to keep you occupied. It will help to take your mind off things. Just play it by ear, and go into it slowly. Take care of you.
I know work helped me when I lost my sister.

Your new job was kind enough to change your start date so it is a sign you need now to put yourself out in the world. Take your time, work helps take your mind off your saddness.

hugs. I'm sorry for the loss of your mother. When my father died, I had been working at a new job for about a month. They were shocked when I told them I needed the week off (my dad died on a Sunday afternoon) and were generally less than helpful about the situation. The fact that your new manager changed your start date gives me hope for you in your new job. I wouldn't be surprised if people don't acknowledge your loss, as they don't know you, and act like business as usual.

I found that there were times when I couldn't distract myself with work, so I would take a break and hide in the bathroom so I could cry a little and then clean myself up before going back to work. Remember that you have to take care of yourself and honor how you are feeling, even if it's at work. I also suggest you take a lot of notes about the details of your job while they are being explained to you, so you can reference them later on if you have forgotten. I found that I was pretty forgetful for a while after my dad died, especially about trivial things, which my job was.

I eventually quit that position about a month after my dad died, because of a lack of support from my manager. She called me in for a meeting about my "energy levels not being up for the job" (I was office support/front desk at a wellness center, of all things) and I told her this was not going to work out and promptly gave her 2 weeks notice. Oddly enough, when the owner found out I was leaving, she talked to me and stated that she hoped this was not because of my father's passing, because she felt that I would benefit from the healing environment of the center. I told her she needed to talk to her office manager, because that was NOT the message I received from her, and this was yet another example of why I was quitting - the constant lack of communication and mixed messages that the two of them exhibited almost daily. Again, this was a place that was not functioning well as an office to begin with (all the other staff members except for the owner and the office manager have quit since I did, which speaks volumes), so I'm hoping that your experience will be better than my own. Remember to take care of yourself, and if you feel you can't handle starting the job yet, speak with your manager as soon as you can and be open about how you are doing.

I found have only been back to work for 3 weeks, I found that it helps at times, but at others it doesnt. I have found that there are times I just need to go for a drive, or a walk around the bldg. My dad works 3 floors below me so that helps me alot. I am having to take it slow, as I am still having problems concentrating. it sounds like your manager is an understanding person, mine is as well so that will help alot