since you are only taking one or two ... do it whenever.. imo ...

the only usual qualification ... is on flowering shrubs .... is when you might be cutting off all next years flower buds.. if you are giving it a haircut .. and you did it late in the season ...

but since you are leaving a majority of the plant.. unpruned... then this rule isnt really relevant ....

you make your cut.. 3 to 6 inches from the ground.. where ever you can get the saw in there ..... without doing a lot of damage to stuff you are leaving ... the plant will rewspond by triggering 2 or 3 new shoots below the cut ... otherwise known as 'triggering dormant buds'

a good tree saw.. really helps ... and if you have a sawzall ... a TREE BLADE is best .. it really matters.. when cutting thru wet wood.. as compared to dry lumber ..... either should be had for under 10 bucks ...

lilac already has next years buds on them ... and i went to town on one of mine ... mostly because i walked by with the saw ... lol ... and the fact that it was hanging over the driveway and pissing me off ... it only took me 3 years ... but i taught it a good lesson.. on who is actually in charge around here .. lol.. AND I HAVE ABSOLUTELY NO WORRIES ... so you shouldnt ... period ...

ken

https://www.walmart.com/ip/7-Inch-Folding-Utility-Saw-Triple-Edge-Razor-Tooth-Portable-Saw-with-Gear-Lock-by-bogo-Brands/915337201

https://www.homedepot.com/p/Milwaukee-9-in-4-5-TPI-Pruning-Sawzall-Reciprocating-Saw-Blade-48-00-1304/202256181?MERCH=REC--PIPHorizontal2_rr--202256182--202256181--N

Thanks SO MUCH for your detailed advice. And yes, I do have that tree blade. My daughter who is an arborist bought it for me as a birthday present! I use it on a whole bunch of stuff but apparently not my viburnums. Too bad she lives in Montana - I should fly her home to do this job for me!! OK - tomorrow is the day!!

My daughter who is an arborist

==>>> did she already give you this info.. and you didnt believe her ... lol ...

it could be done at xmas.. if she was coming home for the holidays ... whats a foot or so of snow going to make a difference.... lol...

ken

She only advises on trees - and I've saved a boat load of money on all my oaks. All the neighbors come out and watch her climb these monsters. It's quite an art!!