`ssh remotehost "sleep 30000"`;

Never use backticks if you do nothing with the captured output. Use system instead.

$ date; perl -e 'system q{nohup ping -c 5 perlmonks.org &};'; date; sl
+eep 10; date; cat nohup.out
Sat 11 Apr 11:06:34 BST 2020
nohup: appending output to ‘nohup.out’
Sat 11 Apr 11:06:34 BST 2020
Sat 11 Apr 11:06:44 BST 2020
PING perlmonks.org (209.197.123.153) 56(84) bytes of data.
64 bytes from perlmonks.com (209.197.123.153): icmp_seq=1 ttl=57 time=
+96.2 ms
64 bytes from perlmonks.com (209.197.123.153): icmp_seq=2 ttl=57 time=
+95.5 ms
64 bytes from perlmonks.com (209.197.123.153): icmp_seq=3 ttl=57 time=
+95.1 ms
64 bytes from perlmonks.com (209.197.123.153): icmp_seq=4 ttl=57 time=
+94.5 ms
64 bytes from perlmonks.com (209.197.123.153): icmp_seq=5 ttl=57 time=
+95.1 ms

--- perlmonks.org ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4015ms
rtt min/avg/max/mdev = 94.518/95.322/96.248/0.563 ms
$
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