Because the lines to get in to the cloister were massive I joined my times one hour entrance slot queue really early. If you join it late it can take you over half an hour to get down the queue and into the monestary, so joining the queue early wasn't a bad idea. But there was no shade and even though I had put factor 50 sunscreen on I ended up shading my bare arms using the T Shirt I'd bought in PdB as a sort of shawl. As it turns out, the cloisters themselves were a bit of a let down, so I would advise anyone else to just skip them entirely, do the church and eat some tarts.
Note that at this time the Belém Tower was covered in tarpaulins and closed for rennovations, so I didn't get to see much of that.