Ref. No. 41/1003
In the name of Allah the most Gracious the most Merciful
The answer to your question is as follows:
Performing two Rakats of Tahajjud in one unit is better. صلوۃ اللیل مثنی مثنی
And Allah knows best
Darul Ifta
Darul Uloom Waqf Deoband