File sizes varies, for instance, some files have ~300MB, others ~1GB or ~2GB.
My disk is not operating in full capacity while running awk, so I think your solution to read multiple files at once will benefit me.

Although I can't tell what's the datetime just by file name, I can leverage the fact that log files are ordered to choose what files i'll be reading, like it was suggested here. I'll make an exampĺe to illustrate.

I have 832 files in one directory totalizing 100GB, let's say nginx1.gz, nginx2.gz, ..., nginx832.gz.
first line of nginx1.gz has [11/Jul/2018:18:00:01 and the last line [11/Jul/2018:21:00:01
first line of nginx2.gz also has [11/Jul/2018:18:00:01 and the last line [11/Jul/2018:21:00:01

The natural would be nginx2.gz start with the same time or later than nginx1.gz
I could do what you've suggested with this code:

Code:

        gunzip < "$FILE" | awk '$3 > "[20/Jun/2018:22:00:00" { exit } ; {...}'

, but I would avoid to read just 2 hours of logs. So, I thought of reading the first and last line of each file and decide whether I would read the file or not. For instance,
1st line datetime would be in: zcat file1.gz | head -n 1
last line datetime would be in: zcat file1.gz | tail -n 1

So, there are two cases when I could skip reading the files:
1 - When 1st and last line is before the time I want
2 - When 1st line is after the time I want (like you've suggested)

This way I think it'll be much faster. I've finish this modification and I'm testing it right now.
If everything is allright I'll test your solution of reading multiple files at once and give you the feedback of the results.

Thank you very much for your help, I didn't know about wait and it'll probably help me.