As time passed.. could be 'over time' as in
'over time, Bob and Daisy got to know each other...'
How about being more specific but evoking time passing in your writing - like 'during the Fall Semester...' where previously you had let us know we were in Spring, perhaps by having earlier mentioned the smell of Spring flowers in the grass. Or you could be more poetic like,
‘Bob kicked the fallen leaves with his foot restlessly as he turned to Daisy on the park bench.. “Daisy...” ’
You could say:
- as Winter turned to Spring...
- ‘As the nights became colder’ or ‘began to draw in’
- As the trees began to show their Autumn colours.
- Sitting by a fire, drinking egg nogg
Using the seasons can help you, and, as relationships have their own seasons, might be a fun way for you to position your characters, and their relationship, in time.
Think of Summer, with its tennis, grass, ice-creams, beach, swimming costumes, football games - maybe using events, like the Summer Prom (i.e - any event that we know usually occurs at a certain time of year) or Christmas, to let us know where we are at, in time.
Think about what we wear at different times of year
‘Daisy's pretty floral dress fluttered in the Summer breeze, as Bob...’
If more time passes, your characters can even change themselves - to let us know where we are at in time: As Daisy reached up to kiss Bob, he seemed a little taller, more mature, than when they'd first met 6 months ago...
So what I'm suggesting is that you let us know, creatively, where we are in time, instead of only using expressions, as I think it will be more fun to read - and hopefully, more fun for you to write, too! For, aren't you really asking 'how may I not bore you, the reader, with repetition?' - so, this is how!
Ultimately ‘Daisy turned and saw Bob across the square. His blue eyes were wrinkly now, and a grey streak at his temples gave him an authoritative appearance that was appropriate – for he was now the Dean of the college.’
I hope that you enjoy this, and have lots of fun, writing...