Is there significance to length in a matched transmission line?
In the ideal case, where source, line and load all have the same impedance, there is no significance to the length of the line, other than loss (shorter is better).

Where tolerances make the impedances depart from ideal, there will be small effects, but unless you know which way the departures are going, it's not possible to say whether you will be better off with any specific length.

If the source and load are well controlled, and the line is poorly controlled, then you will be better off with multiples of \$\frac{\lambda}{2}\$ line length. This length transforms the impedance at one end of the line into the same impedance, regardless of the line impedance.

If the source deviates down, and the load deviates up, or vice versa, then an odd multiple of \$\frac{\lambda}{4}\$ would be better, as that length of line transforms Zload into \$\frac{Z_{line}^2}{Z_{load}}\$ at the source end.

However, for either of these cases, you need to have enough control over the impedances to know how wrong they are, and if you know that, you might as well make them correct, or tune for them properly.

The only other case to note is that if the connection line is very short, say less than \$\frac{\lambda}{10}\$ (and the shorter the better), errors in the line impedance will have little effect.

To check your line width calculations, a 50ohm microstrip on FR4 is roughly 2 substrate thicknesses wide.

It's worth noting that the impedance can be fairly wrong, before significant reductions in power transfer between source and load occur. A quick simulation on SPICE may be worth doing to give you an idea of the permitted tolerances.