Go to Top 16. Unopened with an unbroken seal, the solution will last one year. Opened, but placed in an airtight container, the solution will last six months. Opened and exposed to air, the solution will last one day. Standards below 100 uS will degrade at a faster rate than others due to air.
Evaporation drastically increases conductivity values.
Go to Top 17. No, you cannot place one manufacturer's probe on another manufacturer's meter. The cell constant may be different and the pin configurations are usually different. The type of thermistor used for temperature compensation is usually different also. The cell constant is not a big problem, but not matching the pin configuration and temperature compensating element used would be a problem.