R_za is correct - Immgration clearance times in Jakarta (especially for foreigners) can be very long- over an hour (or More) depending on what time your flight lands & how many others are coming in at the same time & how many immigration officers are on at that time. You could also get really lucky and be through in five minutes - no way to know. If your flights are during Ramadan which is May//June this year I would not risk it as there can be less people working as people take leave.
Also know that @ T3 depending on which gate your plane comes in on it can be a 10 to 15 minute walk before you even get to immigration. Baggage services can also be slow in Jakarta - no rhyme or reason to which airline or which day or how long it will take at any given time.
I am based in Jakarta, feel free to send me a message if you have any specific questions