Filter and add extra fields in the pcap

edit

That is a generated field which Wireshark creates from data in the packet.
You could maybe store it in a packet comment if the file is saved in pcapng format.

packet-http.c
-------------

 { &hf_http_time,
   { "Time since request", "http.time",
    FT_RELATIVE_TIME, BASE_NONE, NULL, 0,
    "Time since the request was sent", HFILL }},

if (! nstime_is_unset(&(curr->req_ts))) {
    nstime_delta(&delta, &pinfo->abs_ts, &(curr->req_ts));
    pi = proto_tree_add_time(http_tree, hf_http_time, tvb, 0, 0, &delta);
    proto_item_set_generated(pi);
}

Yes i need it to be saved additionally to the data from the packet for example as you said in a comment you thing that it is possible ?

I'm not sure what other tools you'll be using to process the pcapng, they may not handle comments.

Comments or in custom http header also would be interesting option

Adding/appending packet comments in pcapng file with the Lua API: here they started with Lua but after discussion looks like editcap and a shell script may be a good solution.

Other ideas here