This one's easy.
Just take your age and your investment goals, and ask yourself 'how long can I leave my money tied up?' Then you'll be able to figure out your investment time scale.
Of course there are many different factors, if you're a spry 58 year-old looking to make some cash by the time you retire, your Time Scale will look a lot different to a 30 year-old with the same plan. This is why investment time scales are usually split into three types:
Short-term - 1 to 5 years
Medium term - 5 to 10 years
Long-term - 10 years +
You need to ask yourself:
"How long can I leave my money tied up?"
Different products suit different investment time scales:
0 to 5 years - Capital guaranteed products such as savings accounts, (mini) cash ISA, fixed rate bonds
5 to 10 years - Medium risk products such as corporate and government bonds
10 years + - Higher risk products such as equities
More importantly, no matter what the time scale is, the appropriate investment product depends on the amount of risk you're comfortable with.
"Remember the longer your time scale the more likely you'll be able to meet your investment goals."