An essential step in winemaking is to remove / siphon the wine off the sediments (lees, dead yeast cells) into another clean secondary, wine barrel, and repeat after another one or two months (depending upon the wine and style) and again before bottling.
This procedure is called racking. It is done when necessary, not just two or three times as stated above. The rule is, as long as there are fresh deposits on the bottom after a regular interval (30 to 60 days), even if they are just a light dusting, the wine should be racked.
Only when that interval passes and there are no fresh sediments/ lees - can the wine be left to age - or is the wine ready to be prepared for bottling.
It is not necessary that the interval between racking be 30 days, 45 days or 60 days, but it shouldn't be less than three weeks. It is perfectly fine to leave the wine on the lees for three months. Beyond that and the wine enters a danger zone caused by dead yeast cells breaking down - rotting.
While this can cause off-flavours and odours if allowed to go on too long, the bigger danger is the formation of hydrogen-sulfide gas, which smells like rotten eggs and can be the death of the wine. But if the lees are stirred every week or so, neither the off flavours, off odours nor hydrogen-sulfide gas form. Indeed, the wine is actually improved by extended contact with the lees as long as they are stirred frequently.
During racking the wine's exposure to oxygen-lade air should be minimized. Those who are extra cautious can sparge the receiving barrel with carbon dioxide or argon gas before racking the wine into it.
Racking is not as difficult as many new winemakers make it. There is no reason to stress over racking at an exact interval, or leaving the wine in contact with the lees an extra week - or even a month. But it is prudent not to be sloppy about it, and to sanitize all equipment before and after use. Cleanliness in winemaking is everything.