It could be required to modify a default timeout value for requests that apt performing when obtaining package lists and packages itself. As example, the traffic can be inspected on its way and this could increase the delay.
apt has a configuration option that allows you to tune timeouts, but it's weirdly documented.
To add/change timeout, open apt configuration file. The proxy settings is either in /etc/apt/apt.conf or /etc/apt/apt.conf.d/80proxy.conf.
In my case configuration looks like this:
/etc/apt/apt.conf.d/80proxy.conf
Acquire::http::proxy "http://proxy.local:3128/";
Acquire::ftp::proxy "http://proxy.local:3128/";
Acquire::https::proxy "http://proxy.local:3128/";To change timeout setting add these options:
Acquire::http::timeout "240";
Acquire::https::timeout "240";where "240" is a timeout in seconds.
