"The first thing I would do is gather whatever data is available to support my claim that the resource is consistently late in reporting their time. I find that most people with issues like this are sometimes unaware of the frequency and impact of the problem and it helps to be able to provide details when discussing the issue.
The second thing I would do is reach out to them in a comfortable setting. I might invite them for coffee, or lunch, or ask them to take a walk with me. I find that it is easier to discuss issues away from others and on neutral territory.
I would then bring the issue to light and explain the downstream effect to make sure they understand the importance of resolving the issue. From there, I would ask for a commitment and timeframe for change and see if there is anything I can do to assist or make the process easier.
I would then follow-up to make sure the issue was resolved. If it continued, I would remind the resource of our agreement. In the event it still persisted I would schedule a meeting with the resource and their manager to discuss next steps."