I've caught males colored up and on the banks making nests in the first week of April. I've also caught males colored up in 2-3 foot of water the first week of June. So by those numbers more like 2 weeks. The best time to be out is when the water level and weather have been consistent for about 4-5 days. Good luck finding that this year though. I'll be focusing my attention to getting on them later in the month along with the walleye. Fish can and will be caught with these high levels but will be hit and miss. Don't expect to go out and get your limit of 50 in the afternoon. As for the timing the main driver is the amount of daylight. I've read somewhere that they spawn best when the amount of sunlight is between 13.2 hours and 14.7 hours?? 'm not sure if those are the exact numbers but close anyway. Hitting the spawn just right is tough. Out of the month plus it lasts there's only going to be a handful of days that are just really good the kind of days you tell your grand kids about if you know what I mean.