How long does it take for a blocked dopamine receptor to be broken down by the body?
Partial Answer and Suggestions
As @De_Novo says, this is a complicated, albeit very interesting, question. There are various reasons for this, such as the fact that the receptors aren't just internalised but also recycled and the fact that there may be antagonist and dose-dependent changes in receptor internalisation. There's the added complexity that receptors can have their expression changed in the short term (by internalisation) but also in the long term (by varying synthesis). You should then note that there's not a set lifespan of the receptors - there's a statistical distribution for how long they'll last at the membrane.
But I'd quite like to stimulate discussion about it so I'm proposing some smaller questions:

Do irreversible dopamine antagonists change the rates of receptor internalisation, degradation or recycling? This is likely to be the case as internalisation of receptors is often activity-dependent. Also, the shape of the irreversible antagonist could change how the receptor fits into a clathrin-coated pit.
Do the irreversible antagonists change the rate of receptor synthesis?
What mathematical models can describe the dynamics of internalisation? This might be a bit tricky since there are feedback mechanisms here (e.g. recycling --&gt; internalisation --&gt; degradation --&gt; less recycling).
How does the proportion of blocked receptors affect these factors?

By answering these questions (or even by finding an experiment that measures the half life of the receptors with blocking), you could come up with an answer for the half-life of the blocked receptors.