Random is not really nice :/ Let's try AccuracySec

unit-files/backup-u@.service

@@ -6,7 +6,6 @@ Type=oneshot
 TimeoutStartSec=0
 WorkingDirectory=/data/domains/%i/
 EnvironmentFile=/etc/environment
-ExecStartPre=/bin/bash -euxc 'sleep `shuf -i 0-400 -n 1`'
 ExecStartPre=/bin/bash -euxc '/data/domains/%i/BACKUP'
 ExecStart=/bin/bash -euxc ' \
   /bin/docker run \

unit-files/backup-u@.timer

@@ -7,4 +7,5 @@ BindsTo=universal@%i.service
 [Timer]
 OnActiveSec=20
 OnUnitActiveSec=60min
+AccuracySec=50min
 

unit-files/backup@.service

@@ -8,7 +8,6 @@ EnvironmentFile=/etc/environment
 ExecStartPre=/usr/bin/docker run --rm -v /opt/bin:/opt/bin ibuildthecloud/systemd-docker
 ExecStartPre=-/usr/bin/docker kill mysqldump-%i
 ExecStartPre=-/usr/bin/docker rm mysqldump-%i
-ExecStartPre=/bin/bash -euxc 'sleep `shuf -i 0-400 -n 1`'
 ExecStartPre=/bin/bash -euxc '\
   if [ -d /data/domains/%i/mysql ]; then \
     echo "Backing up mysql databases for %i"; \

unit-files/backup@.timer

@@ -7,4 +7,5 @@ BindsTo=web@%i.service
 [Timer]
 OnActiveSec=20
 OnUnitActiveSec=60min
+AccuracySec=50min