Is it permissible to perform Tayammum for prayer when there is not enough time for Wudu due to work circumstances, and is it valid to wipe over the head covering (hijab) without wiping the ears?

What you have mentioned is not a valid excuse for performing tayammum, because ablution (wudu') does not take a long time. Therefore, you must perform ablution for prayer and find the necessary time for it by any means. Hanbali jurists permit wiping over women's head coverings (khumur) that are wrapped under their throats if they were worn in a state of purity. Wiping the ears is a Sunnah according to the majority of scholars, and if you omit it, your ablution is still valid.