You're absolutely right, those spices need more time to extract flavor.
If you add them at or close to flameout, give them a 30' steep/stand before starting the chilling. During the steep your wort will cool down gradually, which is good.
To speed up extraction, grind, pound, or crack (mortar) the coriander coarsely. I even run the orange peel through my spice/coffee mill to get smaller pieces and lots of powder. Those dried peels are very hard and tough. If you can't or don't want to grind them, soak them in a covered cup of hot water for a couple hours (use microwave to heat the steeping potion every now and then, don't boil). Then add the potion, peels and all, at flameout or 5 minutes before, steep 30' and chill.
To give much more and better flavor, lightly toast the whole coriander seeds in a skillet. Only toast them to become a couple shades darker than the green ones, definitely not brown, you're not making Indian curry.
Amounts to use (crushed and pulverized):
I use 1/4 oz (7 grams) of each in a 5.5 gallon batch, that's pulverized and a 30' steep/stand after flameout. You can double quantities of either or both for more pronounced flavor. Putting in a whole ounce each may be about the limit.
7 grams of coriander seeds (whole) is about 2 tablespoons. The (big) bags they sell at the Indian spice stores are great and fairly cheap.
Curacao bitter orange peel is used traditionally, but you could use fresh peel from oranges, tangerines, persimmons, etc. Seville oranges are the most sought after and wonderful. Whole Foods or Trader Joe's have them during the season. You really want the colored zest, don't get too deep into the (white) pith when grating or peeling. You could add some of the juice too.
When adding larger amounts of peel and spices, taste the wort each time, and be careful not to overdo it. Careful tasting gives you an indication on how far to take it. If needed, you can always add more after primary fermentation has completed, similar to a dry hop.