Visuddhimagga XIV-189

Samayavasena ekamuhuttapubbaṇhasāyanharattindivādīsu samayesu santānavasena pavattamānaṃ taṃ taṃ samayaṃ paccuppannaṃ nāma, tato pubbe atītaṃ, pacchā anāgataṃ.

（三）依「时」说：即依于一须臾、朝、夕、昼、夜等的时间中相续而起的色，彼等的时为现在时，从此前面的为未来时，在此后面的为过去时。

Ñ(XIV,189): (c) According to period: any period among those such as one minute, morning, evening, day-and-night, etc., that occurs as a continuity, is called present. Previous to that is past. Subsequent is future.