I am 58 and also grappling with what to do with my TSP funds, especially since they are virtually all non-Roth. With SS @70 and pension I will be in 25% bracket when I hit MRD age, so don't want to be forced to withdraw (I definitely won't "need" those funds to live).
So despite the advantages of very low expense ratios and some unique fund options (e.g., G), conversion to tIRA and then to Roth IRA seems to be the way to go for me. What I'm struggling with now is "how much" and "how fast" to convert because with TSP you have limited options on how you can get funds out. Since I don't have much 'space' to reach the 15% tax threshold and would never get it all converted at that rate, so will need to do larger conversions at least in some years. I-ORP says get it all converted in the first few years.... but I still don't know how fast.
The point is that if it makes sense for you to Roth convert, it may be better to do a partial or total rollover into IRA. Or take the annual distributions in the amount you want to convert. [Note that whether you're paying taxes on the conversion from after-tax accounts or from the IRA funds makes a difference in the calculus -- there are some other recent threads discussing this).
For me, I'm currently thinking about doing a one-time lump sum into an IRA (like 50% of the total?), to give me some flexibility on large conversions in these first few years of semi-retirement when my income is less predictable, and then taking variable distributions from then on (with the latter you can adjusting the monthly withdrawal amount once each year, which I'll do to optimize my tax hit). Note that TSP allows you to combine the withdrawal options, but you can only do one 'lump sum' rollover ever (although as another poster mentioned, there is no 'deadline' to decide to do this as far as I could see).
[FYI, these non-Roth TSP assets represents about 35% of my total portfolio.]