This is too broad of a subject. However, in a nutshell, the major problems in time management is:
- Wrong project estimates in order to meet stakeholders' expectations (that stakeholder can be the project manager or an executive)
- Non-standard estimation techniques (usually this happens when there is no PMO in place)
- Not accounting for risks in project estimates
- Not communicating with HR about the availability of resources allocated to a project
- Having new people on board with no idea about their productivity
Hope that helps!