How long does it take for a SPV to intermittently sync (order of magnitude)?
SPV syncing depends entirely on the SPV servers that you're connected to. They may not have that much bandwidth and you might have a very slow sync, for example.

That said, you only need 80 byte headers per block you haven't seen (about 1000 blocks per week, or 80Kb for every week that your device is offline) and about 500-1000 bytes per UTXO you have (obviously this is highly dependent on how much new UTXOs you've received).

So assuming about 5 tx's per week and 1000 blocks per week, it's less than 100kb download to catch up once a week, which by any measure should be very quick. On most connections it shouldn't take more than 10 seconds.