There is a variety of different coating/finishes used for solder points. Silver, Tin, Gold, hybrids are all common. All depends on need/cost from the manufacturer.
Just solder as normal. Flux, Tin, Solder.
Like everything in engineering... IT DEPENDS
Time, by itself, is meaningless. There are a few competing concerns:
The temperature must reach the melting point of the solder material. This depends on the type of solder, the parts (mass and chemical composition), the soldering iron tip material and shape, power applied to the tip and its thermal conversion efficiency, and the ambient temperature (ex. preheaters).
It's not just about temperature, but how quickly you get there. If temperature rise is too slow, the total energy transferred past the pin to the internal part may be sufficient to damage or derate it. That is why all components come with either a JEDEC/IPC reference profile and/or a soldering temperature profile. This profile is an energy chart showing temperature vs. time.
If you ramp the temperature up too quickly you can get thermal fracturing of the part as the different elements inside expand at different rates breaking free of the ultrasonic bonding or lead frame.
If you leave the iron in contact for way too long you will overheat the part resulting in the destruction of the packaging (plastics don't fair so well, ceramics do much better) and the functional loss of the silicon die inside. There are many failure scenarios for microchips from overheating ranging from the obvious burn-out (physical fault) to the loss of function from ion-migration in the doped-semiconductors.
...but 2 seconds is a good average
The reason you hear 2-3 seconds as a "rule" is that for most parts and most irons and most situations and most PCB's and most... this time value works out safely.
Best Answer
If you're doing hand soldering with an iron, you should only be making contact (and potentially warming the surrounding components) for about 3 seconds. Only the point of contact with the tip of your iron should be reaching temperatures of any concern. Assuming the components you're worried about are also soldered in, there should be no issue or need for further precaution. They can clearly take full solder temp for a few seconds so a brief rise in ambient temperature will be nothing.
Aluminum foil is a marginally useful trick for creating a heat shield when doing hot air rework. You still want to keep it off the components you're trying to protect as much as possible. It should only serve to divert the hot air since it still conducts heat.
Kapton tape's virtue is that it doesn't break down under high temp, and it's available in anti-static formulations. It's great for holding things in place as you solder them, or maybe for holding down the aluminum foil as you do your hot air rework. Borderline useless for heat protection by itself though.