Bit more to it than that.
There will be no noticeable downtime, but it is worth making sure you are not connected over night on the day you are due to switch as that can help avoid getting a stuck profile.
During the first 10 days the system will be tracking your line performance to determine the maximum stable rate for your line and from that the fault threshold rate (70% of MSR). These figures will be used in the future to determine if your line has a fault as a sync below the FTR is considered a fault. Note, that is a sync below that level not a data rate below that level.
The profile for your line determines the data rate and it reacts to changes downward in sync immediately but only to upward changes every 3 days once you are past the initial period.
Once you have maintained a stable sync rate for long enough, one single low sync would be ignorred if it happens, but two will bring your profile down.
Expect a bit of instability during the first few days but it usually settles down pretty quickly to the sort of level you can expect to maintain.
