Concatenate in VBA

I need to use VBA in order to input a formula in each cell of a column (or just the result of a formula) which uses Left/Right and Mid in order to select the components to be concatenated.

In Excel this would look like:

=CONCATENATE(LEFT(B2,2),":",MID(B2,3,2),":",RIGHT(B2,2))

in VBA I need to replace B2 with Cells(intRowCount, 6) where intRowCount increases up to the total row count.

I also want to apply two separate formulae, one if the value of B2 is greater than 2359.59 and one if it is lower.

Unfortunately I keep getting syntax errors.

Please help!