A day or two? Try a minute or two.
It died again almost immediately last night and was unusable despite, after a couple of modem-router re-boots, apparently re-connecting (internet and DSL lamps both lit and steady).
Another re-boot seems to have fixed it this morning, but I have no confidence that it's all over.
I called support back last night; the CSR seemed more willing to carry out extensive checks and after several minutes said he would have to pass it to second line support, citing some evidence of a 'signal delay' as he watched me re-booting from his end.
I don't know exactly what that means and I don't know how quickly it's likely to be fixed. Given the intermittent nature of the problem I don't even know how I'll know it's been fixed.
Anyone got any ideas?