Open means the investigation has started but has not been completed. Back in May 2016 probably took DSS about 4 to 6 weeks to submit your case to OPM for investigation. There's been a 500,000 case backlog at OPM for the past several months. Average case completion times for the fastest 90% of Secret (Tier 3) investigations is 158 days. If you combine these two figures with about 15 days for adjudication you get about 265 days end-to-end. With an average of 265 days the range is probably between 180 days and 360 days for the fastest 90%. If there are moderate to major issues in your case expect a Subject Interview and expect the entire process to take over a year. In addition to the credit check, your current and past supervisors, etc., should have received letter inquiries by now.