It's subjective to say safe or not. My advise is don't. Latest, leave Tanah Rata/Brinchang at 5pm. It will be already dark before you reach Tapah/Simpang Pulai.

With current rainy weather, there are a lot of small landslides here and there, and I've mention it won't publish in newspaper as afraid affect tourism. Those who went up in recent 1-2 weeks, can concur my statement or not.

At night, you won't be able to see small landslides and immediate action/panic, may swerve off-road.

My 2 cents.

If possible, try to leave before late evening. However, you might experience light traffic travelling at night. Tho road vision is reduced, its easier to spot oncoming car. If you are travelling to Ipoh via Sg. Pulai, road condition should not be an issue be it day/night.