Very slow runtimes when datetime is in a certain format

[Edward-Knighton]

Describe the bug Slow runtimes when using snips/datetime or snips/date + snips/time on certain queries where the date and time are in certain formats (see below)

To Reproduce Runtimes below used while training snips/date and snips/time, but got similar values for snips/datetime. Using a query where the beginning is "I need you to schedule a thirty minute project signoff meeting with john price and david scott" this will be represented as X in further examples:

1. "X at 9:30 am" --> 0.034 seconds
2. "X on friday at 9:30am" --> 0.034 seconds
3. "X on September 25th" --> 0.032 seconds
4. "X on Friday 9/25 at 9" --> 1.017 seconds
5. "X on Friday 9/25 at 9:30am" --> 13.171 seconds
6. "X on on Friday September 25th at 9:30am" --> 16.329

Expected behavior

Expect runtime to be much faster

Environment:

• OS: Windows 10 Pro
• python version: 3.8.2
• snips-nlu version: 0.20.2