Since we plan on hiring a van from Cat Tien to Dalat, would it be advisable to just spend a few hours at Di Linh instead of whole day? Or would it be better to find another hire van to Di Linh and Dalat in two days.
I would spend the morning birding in Cat Tien, then drive to Di Linh and bird in the afternoon . Stay the night, so you have another morning. Keep the van, because you need to do a little driving to get up to the pass at Di Linh as well.
Would a full day or half day at Ta Nung suffice?
In my experience, Ta Nung is very birdy in the mornings and rather quiet in the afternoons (even more so than other sites). I'd try to have at least one morning there, but no point to spent a full day. You can always come back, e.g. if you did not find the Crocias previously here or at Tuyen Lam, or you missed out the OB Laughingthrush in Di Linh.
Lang Bian can be a full day and we can do Tuyen Lam Lake in 2 days, one on each side? I do notice many bird songs (at Xeno Canto) as being recorded on the Eastern side of the lake.
Would the map by Henk Hendrik of 2006 here
http://www.birdtours.co.uk/tripreports/vietnam/vietnam-10/vietnam-march-2006.htm of Land Bian, Ta Nung and Di Linh still stand good? Florian, your map on both Eastern side and western side of Tuyen Lam lake are quite comprehensive.
You could indeed bird both sides of Tuyen Lam, I would do so if I had the time.
More recordings on the east side is most likely because the road is only completed on the western side since a few years.
Before, broad-leafed forest could be easier accessed at the eastern side, as described in Hendrik's or my maps. Hendriks path is also shown in
my map, pointers 1, 2, 3 (mine is at scale, so gives a better idea of the distance), so best use both together if you try to go there. On this trail, you have to walk through mainly pine forest for 1-2 hours first, before reaching broad-leafed forest. Also, the trail is not always easy to find. That said, it was my favorite place to bird, so If you don't mind walking a little rough, go for it. You need a full day there.
The new road on the eastern side allows now easier access to broad-leafed forest, which starts very close to the road. So no need for a long walk first to get to this habitat, and that's why for most prefer this side today. Please not that my map is not very accurate for the western side of the road (I did not go there often at the time). Have a look at google maps as well.
Bi Doup peak maybe a bit far off unless
Just to mention that Bi Doup peak is not the same as the road through Bi Doup national park described above by Glenn. You can go up Bi Doup peak, but need to arrange with the National Park. Possible without camping in one day, but a bit of a rush. Great for birding, but all birds can be found close to Dalat, except Indochinese Fulvetta, which is right on the top of Bi Doup.
I just found a local guide who charges US$50 per person for two days for guide and transport on a 7 seater car. With 6 of us, that would be $300 over 2 days. Would that be a better deal then to hire a van for $60 per day and bird on our own? My only concern is missing Endemics or rare species without a guide to point them out to us. We do have most of the endemic and rare species bird song for us to familiarise first.
Prices sound fine both ways. Guiding fee perhaps a bit low, so not sure if its a really good guide. If you want a guide or not is really up to you to decide, can't help with that. Of course a (good) guide increases the chances that you find all endemics (some are a bit tough). But then you said above that endemic hunting is not your main priority, so if you don't mind to miss some, it may be more relaxing and enjoyable (and cheaper) to do your own thing...