Seems I've finally found a source down under for Ammonium Thiosulphate in Powder form (98%) but it's not cheap. I can get 500grams for $65

My understanding to make a 60% solution I would be to mix 600g to 1 litre.

My question then is if I make a 50% solution (with the available 500g) and my recipe calls for 162ml of a 60% solution can I use a 50% solution and either increase the quantity or perhaps increase the fix time?

Or should I just bite the bullet and buy more powder to mix my 60% solution?