I think giving yourself a timeline can make things worse. I did the same thing when my husband passed. I would tell myself that after passing a certain milestone like our anniversary date for instance, that I will feel better. It didn't. In fact, it made it worse because I didn't succeed and then I felt worse and disappointed that I couldn't stick to the timeline. There is no certain time that you can tell your grief and sadness to end. It will come in its own time.
Good luck to you!