Allah mentioned His sovereignty of the Day of Resurrection, but this does not negate His sovereignty over all other things. For Allah mentioned that He is the Lord of existence, including this earthly life and the Hereafter. Allah only mentioned the Day of Recompense here because on that Day, no one except Him will be able to claim ownership of anything whatsoever. On that Day, no one will be allowed to speak without His permission. Similarly, Allah said,
﴿يَوْمَ يَقُومُ الرُّوحُ وَالْمَلَـئِكَةُ صَفّاً لاَّ يَتَكَلَّمُونَ إِلاَّ مَنْ أَذِنَ لَهُ الرَّحْمَـنُ وَقَالَ صَوَاباً ﴾
(The Day that Ar-Ruh (Jibril (Gabriel) or another angel) and the angels will stand forth in rows, they will not speak except him whom the Most Gracious (Allah) allows, and he will speak what is right.) (78:38),
﴿وَخَشَعَتِ الأَصْوَاتُ لِلرَّحْمَـنِ فَلاَ تَسْمَعُ إِلاَّ هَمْساً﴾
(And all voices will be humbled for the Most Gracious (Allah), and nothing shall you hear but the low voice of their footsteps.)(20:108), and,
﴿يَوْمَ يَأْتِ لاَ تَكَلَّمُ نَفْسٌ إِلاَّ بِإِذْنِهِ فَمِنْهُمْ شَقِىٌّ وَسَعِيدٌ ﴾
(On the Day when it comes, no person shall speak except by His (Allah's) leave. Some among them will be wretched and (others) blessed) (11:105).
Ad-Dahhak said that Ibn `Abbas commented, "Allah says, `On that Day, no one owns anything that they used to own in the world.'''