What time horizons for goal-setting would constitute a short-term and long-term investment?

I'd consider anything shorter than 3 years to be short term. Monies needed for such objectives would be best left in guaranteed investment instruments such as short term endowments, high interest savings, SSBs or FDs. Aim for 2-3%.

4-9 years is mid term for me and you'll be able to have a portion of your investments in low-risk instruments like bond funds or very defensive equities. You might walk away with 4-5%.

Anything more than 10 years is long term and you can have more leeway with regards to growth, here, a blended multi-asset portfolio can yield in excess of 5-7% in the long run.

1-3 years is short term. This is usually involving a specific financial commitment that is approaching soon. Like downpayment on a property, renovation, a car, etc.

3-7 years is medium term. This would usually involve a job promotion, paying off liabilities like an education loan or something similar.

7-15 years is long term. This would be a planned increase in lifestyle. Usually planning for a second or third home, or migrating to a new country.

15+ years is very long term. This would usually be education, retirement, or estate planning. You can even have a 100 year investment horizon if you're planning for wealth preservation over multiple generations.