So you're saying in a 3 hour window (considering you used the word hours, and cannot do the morning convoy but only the after one), with 2 free refresh, giving a total of up to 8 times refresh (Initial 3 Convoy options + 5x 30 mins refresh of 3 Convoy options each + 2 free refresh of 3 Convoy options each), giving a total of 24 Convoy options. You're saying in that 24 options, not a single SS appeared?

I find that hard to believe.