For time markers en route remember that 10% of G/S is 6 mins - usually about 9-10 miles for most light aircraft. Another thing I was taught is that most peoples thumbs ( the last part of it) are about 10 miles on a 1/2 mil map, measure yours before you use it though to double check,so you can say a thumb (plus or minus a fraction as appropriate) is 6 mins, a pre marked pencil works even better for this, cut 5 mile then 1 mile marks along the pencil.