lose track of time 忘了时间；都忘记时间了；忘记时间。
lose track 不能跟上...的进展；失去与...的联系；不记得...。
track n.（人踩出的）小道，小径；（人、动物或车辆留下的）足迹，踪迹；车辙；轨道。

【例句】

What he was saying was so complicated that I lost track after the first couple of sentences.
他说得太复杂，我听了开头的几个句子以后就跟不上了。

I've lost track of the number of times he's asked me to lend him money.
我记不起他有多少次问我借钱了。