TcpDump: showing the absolute timestamp (date + time) of pcap file

You can use the -tttt option:

$ tcpdump -tttt -nr tmp.pcap 
reading from file tmp.pcap, link-type EN10MB (Ethernet)
2018-01-19 17:50:43.275918 IP 172.24.0.97.45386 > 93.153.221.29.80: Flags [.], ack 3335572340, win 251, options [nop,nop,TS val 98777655 ecr 230462279], length 0
2018-01-19 17:50:43.287273 IP 93.153.221.29.80 > 172.24.0.97.45386: Flags [.], ack 1, win 285, options [nop,nop,TS val 230464839 ecr 98706059], length 0
2018-01-19 17:50:44.138480 ARP, Request who-has 172.24.0.73 tell 172.24.0.78, length 46
2018-01-19 17:50:45.162482 ARP, Request who-has 172.24.0.73 tell 172.24.0.78, length 46