I haven't found the actual value of the lvl cache-time set by google servers, but I found how to change it. In the ServerManagedPolicy.java
file change:
setValidityTimestamp(extras.get("VT"));
to whatever you like (here to 30 days):
setValidityTimestamp(String.valueOf(System.currentTimeMillis() + (MILLIS_PER_MINUTE * 60 *24*30)));