If the Custom Format is 0.00"h", your actual entry should NOT have the "h" in it!
That defeats the purpose of having the Custom Format adding the "h", if the entry also has the "h" in it.
If the entry already has the "h" in it, then the Custom Format will not touch it anyway, as Custom Formats only work on numeric entries, and if the entry actually has a "h" physically in it, it is actually a Text entry, not a Numeric one.
The actual entry of your cell should just be: 7.5
Then the Custom Format would display it as "7.50h"
To physically remove the "h" for all your entries at once, simply select that column of that, and do a "Find/Replace", replacing "h" with nothing.
And if you do not want to see the "h" displayed, just change your Custom Format to a Numeric one.