Its hard to predict out of the blue. So much depends on the particular med, the dose, when it is taken ; and on the other meds being taken ( and in which doses and for how long ) - a significant number of drugs have effects on enzymes and other body systems so as to speed or delay the break-up and removal of themselves and other drugs. Your prescribing doc is in the best position to guess usefully.
Remember that mood rarely improves in a straight-line steady improvement, and there are usually bumps on the road, and variations from day to day - one hopes the trend is to improvement. And though one day may be Down, the next is likely to be an improvement.
Mood stabilizers usually don't noticeably improve or reduce mood - they act in the longer term, smoothing out some of the more extreme up and down bumps in mood