Just be careful about a routine (manual) schedule. Make sure to adjust it each season.
If we assume that you water pressure is relatively stable, manual schedule will mean that you will add a set amount of water no matter what (Has it been raining? Lets add water…).
If you don’t adjust the schedule each season, you may find that your fountains are using more or less water than your schedule provides. If you are adding more water, it will soon flow over the sides or down the overflow drain. If you are adding less water, your fountains will soon run dry and possibly damage your pump. Since your water needs will change each season (such as you needing more water during the summer as compared to a winter months), having an unchanging schedule will cause issues.
While overestimating water needs (adding more water than needed) is safer as far as protecting your pump, underestimating (adding less water than needed) is easier to correct with an occasional manual water addition.