To be honest, Trapeang Srangae in Roluos is not worth a visit unless you are an unwavering Khmer-temple freak.
"Trapeang Srangae" sounds like "troperng srangaej". Srangae is the Khmer name of a kind of wild rice. A Trapeang is a small lake, particularly a man-made rectangular basin in the surrounding of a temple. Trapeangs are usually situated to the east of horseshoe-shaped temple moats. It is unclear whether Trapeangs were used for irrigation, too.
However, this modern Khmer name makes sense, as the most interesting feature of this former temple, which is completely in ruins, is not the temple proper, but the temple's moat, which is in a very fair condition, and the surrounding typical Cambodian paddy area.
The remnants of Trapeang Srangae can be reached by using a path beginning at Preah Ko and leading to the east. After some hundred metres you have to turn right. Alternatively, you can start at the Bakong main entrance and take the small road in northeastern direction. Only 150 metres behind the tourist restaurant area you have to turn left and to walk a kilometre or so through farmland. In both cases you will recognize Trapeang Srangae only as a small grove. Though this is a real thicket, you will find the temple definitely, because you will not miss - and cannot pass - the moat always filled with water. There is only one access to the "temple island", and this is from the east, where you should expect it to be, if you are an Angkor enthusiast.
You will only see ground walls, of a Gopuram or a firetemple structure, and then of three former Prasats in a north-south-row. As already mentioned, the architecture is not at all amazing, but you can look for stone slabs with inscriptions or carvings on the ground - or for snakes and spiders.
No time of the day can be recommended here. An Angkor ticket is required for neigbouring monuments in Roluos, but not for visiting the few stones in the thicket called Trapeang Srangae.