I feel the need to admit something. Despite god-knows-how-many visits to Whipsnade and even more visits into the capital, I've never actually been to London Zoo. Something which I'm planning to fix this Friday, mainly due to the new reptile house.
Just wondering a few things for those better acquainted with the collection and the zoo - notably, the best order to see things (I'm arriving midday which is a change from my normal opening time starts), the things to definitely not miss and the best times to see any animals. I'm hoping around 5 hours will be sufficient to absorb the entire site and conclude unnecessary opinions to then post here. Any information would be greatly appreciated
One must-see area that is easy to miss is the Eastern Aviaries below Gorilla Kingdom (represented by a hawk on the map) - they house some lovely species such as African Harriers and the nation's only Asian Woollyneck Storks. Personally, I would make my way here first, as it leads you directly to SLoRA, although as mentioned by
@JVM , Gorilla Kingdom then SLoRA is an equally viable strategy. Between the former Reptile House and former Aquarium, behind the bathrooms and kiosk, is a small vivarium for Europe's only Congo Caecilians with a few more in semi-offshow vivariums behind, which is worth investigating, although your chances of actually seeing them is incredibly slim. Another area is the nocturnal display housing Aye-aye and Grey Mouse Lemurs (separate to 'Night Life,' the zoo's main nocturnal house, which often confuses first time visitors), which can be found at the end of the Ring-tailed Lemur walkthrough, tucked away to the right of the Lac Alaotra Gentle Lemur enclosure. JVM is right to say that the best time to see this lovely but secretive species is usually close to the end of the day.
In SLoRA, make sure to see the only Lake Oku Clawed Frogs in Europe, as well as the Sardinian Brook Salamanders, Telfair's Skink, Big-headed Turtles and Ethiopian Mountain Adders which are all major rarities. The turtles can be difficult to see but are most commonly found beneath the rocks in the centre of their enclosure. As it is new, there are a lot of staff patrolling SLoRA, and most of them are quite helpful and friendly, more than willing to help you find certain species if you are struggling.
In Blackburn Pavilion, be sure to spend some time in the two main walkthroughs looking out for rarities such as Scarlet-chested Sunbird, Splendid Sunbird, Collared Trogon and Ultramarine Grosbeak. The Scarlet-chesteds can most commonly be seen at the feeders and nests at either back corner of the exhibit, but with some luck you may be able to find them darting about elsewhere. If you are struggling to find the trogons (which is more likely lately as they have been spending more time in the offshow area), then they have a second aviary beside the entrance to the first walkthrough where they can usually be seen more clearly. Other rarities within these smaller aviaries include Purple-naped Lories (against the wall of the main walkthrough) and Javan Green Magpies, in an outdoor aviary near Land of the Lions. The magpies are just about impossible to see but are usually most active around late morning.
Monkey Valley has rather inconvenient opening hours of 10:00 to 12:00 and 14:00 to 16:30, and often times the colobus are all indoors so the walkthrough is desolate and there is little point going in. As such, if you are in Into Africa and you look across the Regent's Canal to see active colobuses and people within the walkthrough, then I would suggest visiting as it may be your sole chance for colobus activity.
Enjoy your visit!