It depends on the perennial and what you cut away. If the plant grows from the root then by all means cut away the old dead growth. If it's shrub like or a vine then leave it alone until it buds out. because some shrubs and vines like clematis bloom on last years growth.

Without knowing what plants you have it's hard to give advice but the above it a general rule of thumb

As days warm (and they've been almost hot), it seems a good time to me to go out and clean out foliage that is now dead (but wasn't in mid to late fall), and cut down old stems, and the like...but then I'm intimately familiar with my plants. For someone less so, waiting a bit might be good.

For instance, both of my newly planted (last year) Oenetheras have new growth on the old stems (MO primrose and Sundrops). It would have been a bad idea for me to have removed them last fall...and I didn't.

On the other hand, I have some coreopsis lanceolata (which my friend calls a weed...and she's not far wrong), that are now greening up considerably...but they look like shaggy mops or clumps of football mums. I didn't cut them back as they were still green (in the fall), and I think I should have...and now it's sorta too late, because they're in growth again...no telling how big and floppy they will be this year. They would have been much tidier if I'd ran the weedeater over them in late fall...we'll see how badly I regret not doing it.

For me in a much colder area, the time to clean up most perennials is any time during the cold months that my being in the garden is unlikely to do damage to soil structure and there isn't snow. So I avoid working in beds that don't have stepping stones if the soil is wet and unfrozen. Most years that means I work through some time in November and then start up again in March, but this year has been unbelievably warm in the northeast so I am now working on cleaning up what I didn't get done in the fall. Yesterday since much of my snow is gone and the ground is still frozen, I got out the hand hedge shears and cut back hard prune/type 3 clematis, and removed dead stems and leaves from many perennials, including Iris, mums, Corepsis and Helenium. My type 2 clematis I prune back when I can see what was winter killed, but you shouldn't need to prune any type 1 or 2 clematis until after blooming if at all. A few weeks ago I cut back the few tall Phlox I hadn't gotten to earlier to remove any potentially diseased plant parts. I always leave plants like western Agastaches (which tend to rot if stems are pruned earlier) until the weather warms and they start growing in spring, but everything else that needs cleaning up gets done as time and weather allows. I am more likely to leave until last those plants that have ornamental seedheads or that the birds enjoy, and in the fall I start with plants like Hosta which has foliage that dies with the first frost, followed by those that have the potential to carry disease into next season. Personally, I am not a fan of using power tools for pruning back plants, though I often read of folks using weedwhackers and lawn mowers to cut back perennials. My old-style hand hedge shears are neat, quiet, and quick, and I appreciate whoever suggested using them in a tools thread several years ago. Much faster than hand pruners!

My clay soil is squishy soggy wet. I won't walk around in my garden for at least a month, no matter how untidy it looks. Hope your yard drains better than mine :)

My yard used to be wet like that but a few years ago I regraded it to create swells away from the house, then dug in French drains with drain tile and gravel, and it's helped considerably.

as far as the plants, right now I only have some basics including Shasta daisy, purple coneflower, rudbeckia goldsturm, sneezeweed (Helenium), and swamp sunflower. These look pretty much like dried dead stalks, and some have some green basal leaves poking out. I also have an area of lance leaved coreopsis which I just planted with plugs in the fall and those are greening up too. I like that description of "weedy" because I have some space I'm hoping they fill. Oh I also have some baby baptistas.

so it sounds like I can safely trim the old stalks down now, but also, no harm will be done by leaving them in place until... Middle of March or so? (Last freeze date)

Some folks scatter spring bulbs among their perennials so they feel an itch to get right out and clean up the old perennial foliage - gotta show those crocus and daffs to their best advantage. Some of us feel an itch to get out and putter in the garden that we call spring fever. Your perennials can easily wait until mid-March, whenever there's a warm, sunny day: its the gardener who can't wait.

Anything that typically dies back to the roots can be cut back to the ground now. You should cut down perennials prone to powdery mildew as soon as possible. Also cut down things near bulbs now, before the bulbs start sprouting...you don't want to injure their new sprouts accidentally. Avoid walking in the beds when the soil is mushy.

The only thing you should wait on are the western Agastaches; it's still early and I've seen them die if a cold, wet spell hits after they've been cut back too early.

That's also said to be an issue with the salvias as well (see above). And as a general rule, for any border line hardy plant.

That said, I usually clean when I want to.

I also clean when I want to. If you're comfortable out there and are not losing a shoe in the mud of your garden beds you're probably fine. I cleaned out around the snowdrops and early bulbs already last weekend and it's been down into the teens since, and this weekend I'll do more of the same and will be quite pleased with myself :)