The funny thing about speech and debate is that rules vary on the tournament. Above all, always read the rulebook!
In general, pre-prepared events are not permitted to have a timer. This may change if it is an online tournament.
However, pre-prepared events may, to varying degrees.
Almost guaranteed. Phones are typically allowed as timers, as long as they are in airplane mode.
Sometimes. At times, competitors may not have a timer, but judges can give hand signals (at six minutes left, five, four, three, two, one, thirty seconds.)
It depends. Typically, competitors may have a timer.