The "BLE rules" you refer to would be the "Core Specifications" of the Bluetooth Special Interest Group (Bluetooth SIG). As far as I know, they do not place a limit on how infrequently a device can advertise.
But you may run into problems connecting, if using a smartphone as your central device. Although you might guess otherwise, scanning uses almost as much instantaneous current as transmitting, and since it runs much longer than transmitting, it is a greater consumer of battery energy. As a result, the smartphone OS generally only scans for a limited period after each request. You can, of course, bypass this by repeatedly requesting a scan, but the battery life will suffer.
Focusing back on your peripheral, you should calculate a power budget to determine how much battery energy is consumed by the periodic advertising versus the baseline current draw during sleep. Even though advertising draws several mA, it only lasts a few mSec. Once the advertising interval is longer than a few seconds, you will find the sleep current, even at a few microAmperes, takes a bigger part of the energy budget than advertising.
Also, instead of advertising and scanning, consider maintaining an actual connection, with a long connection interval, and a high value for "slave latency" (number of connection intervals the peripheral is allowed not to respond, without breaking the connection). This tends to optimize battery life for both the peripheral and the central device.
