All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.
We believe that placing that clock in the Mihraab could distract some of the worshippers during prayer and affect their Khushoo‘ (humble submissiveness), and it has been reported in the Sunnah that it is recommended to remove anything that could distract worshippers during the prayer. ‘Aa’ishah said, “The Prophet once prayed wearing a garment with printed marks. He looked at its marks, and upon finishing the prayer, he said: "Take this garment of mine to Abu Jahm, for it turned my attention just now in my prayer."” [Al-Bukhari and Muslim]
Imaam An-Nawawi commented on the above mentioned Hadeeth saying, “This Hadeeth encourages the worshipper to observe Khushoo‘ and have an attentive heart during the prayer, ponder over all we have underlined, and abstain from looking at anything that distracts his attention and concentration during the prayer. It is also derived from the Hadeeth that the worshipper should remove anything that he fears might distract him and hinder his Khushoo‘. It is also inferred that it is disliked to decorate the mosque's Mihraab, walls, carpets and the like with anything that distracts the worshippers because the Prophet highlighted the reason behind removing this decorated clothing in the Hadeeth, i.e. distracting him during the prayer.” [Commentary on Saheeh Muslim]
Moreover, Al-Haafith Ibn Hajar said, “Inferred from this Hadeeth is the dislike of anything that distracts from prayer such as dyes, decorative motifs or the like.” [Fat-h Al-Baari]
Ibn Qudaamah said, “It has been reported that Mujaahid said, "‘Abdullaah ibn ʻUmar used to remove anything between him and the Qiblah, be it a sword or a copy of the Quran." This report was transmitted by Al-Khallaal with its chain of narration. (Imaam) Ahmad said, "No scripts should be written on the walls of the Qiblah in the mosque because this distracts the worshippers who may get preoccupied with reading the scripts during the prayer. It is also disliked to decorate mosques or use anything in them that could distract the worshippers during the prayer."” [Al-Mughni]
Allaah Knows best.