When the watch first made its appearance in PV, it was at the Dubey's house, alerting Arati of the return of Prashant. At that time too, although she did not know that Prashant had returned, the watch still had a strangely distressing effect on her. She mentioned to Shobha that the sight of the watch itself was stressing her out, and that the doctor had warned her about not getting stressed. Today also, the sight of the watch rattled her, and goaded her to act impulsively in a kind of a Hitchcock mystery way. I am thinking of Hitchcock's film called Marnie, in which the main character of the same name, perfectly poised and in full possession of herself, totally loses it whenever she sees the color red. Later, thanks to her husband who researches into her psyche, it is revealed that her extreme reaction to the red color is due to a traumatic incident in her past, where as a small child she witnessed the murder of her parents.
Arati's unchecked reaction to the watch, although on a much lesser scale, is similar. For her, the watch symbolizes the bitterness and trauma of betrayal and abandonment, a core issue that she has had to deal with all her life as an orphan, which was forcibly reenacted in Prashant's breaking off their marriage at a time when she was most vulnerable, and when she needed him the most. Ironically, the very watch that was supposed to mark time, pleasantly anticipating the strengthening of their bond through the arrival of Ansh, instead became a death-knell of the relationship, and a harbinger of lonely years of empty longing and never-fructifying anticipation symbolized by the slow passage of time.
The unprocessed shock and pain associated with all that the watch symbolizes is too much for Arati to bear, and causes her to behave uncharacteristically whenever she encounters it. It is human nature to avoid the unpleasant, and from Arati's standpoint, it is much easier to deny the past rather than to come to terms with it. Destiny sometimes has other plans. The more one avoids something, the more it is in one's face. In another stroke of irony, the watch follows Prashant, by making its own stealthy entry into the Scindhia Mansion, via the hands of the chauffeur, who has become the sarathi, the driver/driving force of Arati's destiny . The order in which the watch made its entry is important, because Prashant preceded it, which symbolizes that with his entry time is starting to run out for Arati's denial and suppression of the past.
The timing of the return of the watch is also significant in that Arati finds herself in a similar crossroads now as she did when Prashant left her, shortly after being gifted with the watch. Then, as now, Arati was in love, was vulnerable as she was pregnant. It is no wonder that the watch evokes images of losing the very core of her being and security. Then it was Prashant; now it is Yash.
In anger and fear of her uncontrollable emotions, Arati flings the watch on the driveway, trying unsuccessfully to deny and erase the pain of a past that just will not go away. The watch lands face down, with the glass shattered, which means that the unraveling past is discovered and by Yash.
That he wanted to return the watch to Prashant with an apology on Arati's behalf is an interesting closure. In keeping with the scheme of this symbolism. Yash appears to indirectly be apologizing for Arati's having moved on in time, while Prashant still is hanging on to the broken opportunities in the past that the shattered watch now represents.