If you have never done one then hard to say. Give yourself a full day and you should be OK.
So long as all the bolts play ball I could change one in under two hours if time was of the essence. However I have all the tools and have done more than 10 TD5s before.
I would allow myself half a day including stopping for a cup of tea and some biscuits. You are supposed to wait for the sealant to cure between the head and cam carrier before starting the engine. Make sure you have everything you need before starting and keep everything very clean. Bag and label stuff as you remove it if you are not familiar with where it will all have to go back. Also make sure you know all the torque and adjustment settings. Guessing here is not really an option unless you really have no choice. Do not drop anything down the timing chain opening as that will require major dismantling to retrieve it. While the head is off give the bores a good inspection and clean the tops of the pistons if they are particularly dirty. If confident you can also check the valve seats and lap them if necessary while the head is off.