Will he serve full 25 days before deportation

In most cases, yes, he will serve close to the full 25 days, but there can be small variations.

Here is how it usually works:

Short sentences like 25 days:

• There is often little or no time off for good behavior
• Some facilities may apply a small amount of credit, but it is not significant on such a short sentence

Possible ways he could get out a little earlier:

• Good time credit (if the facility applies it to short sentences)
• Overcrowding or administrative release (not guaranteed)
• Transfer to immigration custody (ICE) before the full time is completed

That last one is important. Sometimes:

• Immigration places a hold
• The jail releases him directly to ICE custody
• He may leave the jail before day 25 but is still not free, just transferred

Deportation timing:
Deportation does not always happen immediately after sentencing. It can:

• Happen after he finishes the sentence
• Or after transfer to immigration custody

Bottom line
He will likely serve most, if not all, of the 25 days. The only real chance of getting out earlier is if he is transferred to immigration custody before the sentence is fully completed.