You should add time terms if you want to know 'when i drink that'.
For examples: "Saya minum kemarin." means I drank yesterday. (Past)
"Saya minum sekarang." means I drink now. (Present)
"Saya minum nanti." means I will drink later. (Future)
And also for verb-ing: "Saya sedang minum sekarang." means I am drinking now. (Present Cont.)
"Saya sedang minum kemarin." means I was drinking yesterday. (Past Cont.)
So, if it just "Saya minum" we will never know when exactly 'when i drink that' except we ask him. But, usually "Saya minum" can be assosiated to Present terms, either Simple Present or Present Continuous (even without "sekarang" terms).