Temporary usage. Use your stove outlet or put 3=way switch and outlet on hot H2O power supply.
If your oven uses 50%+ of the available amps available on its 220-240v circuit, you'd be violating the national electrical code by adding another appliance to the same circuit. Also, if the 2 appliances together need more max amps than the circuit offers, that's an obvious clue you shouldn't be piggybacking on the oven's outlet.
You have to consider both the circuit breaker amp rating AND the wiring gauge used for the oven's circuit. Even if the breakers are more than double the oven's max amp usage, the wiring may only be capable of safely delivering the max amperage for one appliance.
All 220/240 appliances should be on their own dedicated circuit. If for no other reason than to separate them by circuit breakers that only permit the max amps per appliance. So, if the oven needs 40A, and the freeze drier only needs 20A, operating the 20A device alone means you're allowing 150% the max number of amps on that circuit. If there's a malfunction in the drier, the circuit breaker may not trip soon enough to prevent damage to the device, damage to the electrical system/wiring, or a fire.
There's a reason we don't put 100A breakers on all circuits. The wiring isn't able to handle it.
For reference: on most home circuits,
14 gauge wire is used for up to 15A, which includes most standard receptacles and lights.
12 gauge wire is used for 20A circuits, which is normally used for kitchen, bathroom, outdoor receptacles, 120-volt air conditioners, ...
10 gauge wire is for 30A circuits, for things like electric clothes dryers, 240-volt window air conditioners, electric water heaters, ...
6 gauge is used for 40-50A circuits, for cooktops and ranges.
4 gauge is used for 60A circuits, for electric furnaces, large electric heaters, ...
Each time you increase the gauge of wire from one to the next larger (smaller gauge number), you almost double the cost of the wire. Therefore, home circuits normally use only the size wire needed for the circuit breaker installed. If you replace a 30A breaker with a 40A, it doesn't mean the circuit is safe to operate a 40A combined load.
Long story short, don't take shortcuts. Run a dedicated 240v circuit for new 240v appliances. If you can run the wires yourself, that's the hardest part. You'll also need to make sure there are 2 vacant breaker positions in your breaker box, as 240v circuits work by combining 2 x 120v connections. If you look at the oven breaker you have now, it should have 2 x 40A or 2 x 50A breakers with the switch levers connected together so you turn both breakers on/off together. If you don't have 2 vacant 120v breaker slots side-by-side, you might need to rearrange some of the existing breakers or combine low-amp circuits to make room.