I'd say the Perennials can go out anytime now... are you even COLD yet? we are barely up here in zone5 [Illinois] - it just hit us a few days ago.
and your annuals can go out about 6-7 weeks before your "spring" hits... and these days, who knows when that is...
Not that I will know the answer anyway, but the USDA Zone doesn't help tell "when" very much. My PNW Zone 8a is nothing like Texas' Zone 8a, when it comes to gardening calendars.
More helpful would be knowing first and last "average" frost dates.
Some rules of thumb:
The first few times you WS, start with "easy" seeds opr at least some easy seeds. Just so you know that you were MOSTLY successful!
If the seeds need cold-moist stratification or temperature variation, it has to go below 40'F for most seeds to consider it "cold". Each species that needs cold-moist stratification needs it for a different number of weeks (say 2-12 weeks). But 2-6 weeks ought to be enough for MOST species.
If your spring (or winter) is prolonged and variable, watch out for warm spells that cause germination, fopllowed by cold spells that kill TENDER annuals or perennials. Get them into shade during premature warm spells, or get your jugs into a cold frame after they sprout prematurely. Or sow more jugs.
Once air temp is warmer than "really cold", beware sunny days. Either open the lids on sunny days, or make sure you have BIG vent holes to prevent solar heating from sprouting your seeds WAY too early. If you have an ambiguous, lengthy transition from deep winter to mild spring, you might want to keep all your jugs in shade, or at least afternoon shade, until you have no fear of late cold snaps.